Add missing instructions to make test passed (#2100)

[etc/vim.git] / tests / test_black.py

diff --git a/tests/test_black.py b/tests/test_black.py
index 86175aad3041c331680ead5fc92dcabf72a0717b..c603233efc40b58e874e5c76461ee74f6f491ded 100644 (file)
--- a/tests/test_black.py
+++ b/tests/test_black.py
@@ -1,82 +1,67 @@
 #!/usr/bin/env python3
 #!/usr/bin/env python3

+import multiprocessing

 import asyncio
 import logging
 from concurrent.futures import ThreadPoolExecutor
 import asyncio
 import logging
 from concurrent.futures import ThreadPoolExecutor

-from contextlib import contextmanager, redirect_stderr
-from functools import partial, wraps
+from contextlib import contextmanager
+from dataclasses import replace
+import inspect

 from io import BytesIO, TextIOWrapper
 import os
 from pathlib import Path
 from io import BytesIO, TextIOWrapper
 import os
 from pathlib import Path

-import re
+from platform import system
+import regex as re

 import sys
 from tempfile import TemporaryDirectory
 import sys
 from tempfile import TemporaryDirectory

+import types

 from typing import (
     Any,
     BinaryIO,
     Callable,
 from typing import (
     Any,
     BinaryIO,
     Callable,

-    Coroutine,
+    Dict,

     Generator,
     List,
     Generator,
     List,

-    Tuple,

     Iterator,
     TypeVar,
 )
 import unittest
 from unittest.mock import patch, MagicMock
 
     Iterator,
     TypeVar,
 )
 import unittest
 from unittest.mock import patch, MagicMock
 

+import click

 from click import unstyle
 from click.testing import CliRunner
 
 import black
 from black import Feature, TargetVersion
 
 from click import unstyle
 from click.testing import CliRunner
 
 import black
 from black import Feature, TargetVersion
 

-try:
-    import blackd
-    from aiohttp.test_utils import TestClient, TestServer
-except ImportError:
-    has_blackd_deps = False
-else:
-    has_blackd_deps = True
+from pathspec import PathSpec
+
+# Import other test classes
+from tests.util import (
+    THIS_DIR,
+    read_data,
+    DETERMINISTIC_HEADER,
+    BlackBaseTestCase,
+    DEFAULT_MODE,
+    fs,
+    ff,
+    dump_to_stderr,
+)
+from .test_primer import PrimerCLITests  # noqa: F401
+

 
 

-ff = partial(black.format_file_in_place, mode=black.FileMode(), fast=True)
-fs = partial(black.format_str, mode=black.FileMode())

 THIS_FILE = Path(__file__)
 THIS_FILE = Path(__file__)

-THIS_DIR = THIS_FILE.parent
-EMPTY_LINE = "# EMPTY LINE WITH WHITESPACE" + " (this comment will be removed)"
-PY36_ARGS = [
-    f"--target-version={version.name.lower()}" for version in black.PY36_VERSIONS
-]
+PY36_VERSIONS = {
+    TargetVersion.PY36,
+    TargetVersion.PY37,
+    TargetVersion.PY38,
+    TargetVersion.PY39,
+}
+PY36_ARGS = [f"--target-version={version.name.lower()}" for version in PY36_VERSIONS]

 T = TypeVar("T")
 R = TypeVar("R")
 
 
 T = TypeVar("T")
 R = TypeVar("R")
 
 

-def dump_to_stderr(*output: str) -> str:
-    return "\n" + "\n".join(output) + "\n"
-
-
-def read_data(name: str, data: bool = True) -> Tuple[str, str]:
-    """read_data('test_name') -> 'input', 'output'"""
-    if not name.endswith((".py", ".pyi", ".out", ".diff")):
-        name += ".py"
-    _input: List[str] = []
-    _output: List[str] = []
-    base_dir = THIS_DIR / "data" if data else THIS_DIR
-    with open(base_dir / name, "r", encoding="utf8") as test:
-        lines = test.readlines()
-    result = _input
-    for line in lines:
-        line = line.replace(EMPTY_LINE, "")
-        if line.rstrip() == "# output":
-            result = _output
-            continue
-
-        result.append(line)
-    if _input and not _output:
-        # If there's no output marker, treat the entire file as already pre-formatted.
-        _output = _input[:]
-    return "".join(_input).strip() + "\n", "".join(_output).strip() + "\n"
-
-

 @contextmanager
 def cache_dir(exists: bool = True) -> Iterator[Path]:
     with TemporaryDirectory() as workspace:
 @contextmanager
 def cache_dir(exists: bool = True) -> Iterator[Path]:
     with TemporaryDirectory() as workspace:


@@ -88,27 +73,29 @@ def cache_dir(exists: bool = True) -> Iterator[Path]:
 
 
 @contextmanager
 
 
 @contextmanager

-def event_loop(close: bool) -> Iterator[None]:
+def event_loop() -> Iterator[None]:

     policy = asyncio.get_event_loop_policy()
     policy = asyncio.get_event_loop_policy()

-    old_loop = policy.get_event_loop()

     loop = policy.new_event_loop()
     asyncio.set_event_loop(loop)
     try:
         yield
 
     finally:
     loop = policy.new_event_loop()
     asyncio.set_event_loop(loop)
     try:
         yield
 
     finally:

-        policy.set_event_loop(old_loop)
-        if close:
-            loop.close()
+        loop.close()
+
+
+class FakeContext(click.Context):
+    """A fake click Context for when calling functions that need it."""
+
+    def __init__(self) -> None:
+        self.default_map: Dict[str, Any] = {}

 
 
 
 

-def async_test(f: Callable[..., Coroutine[Any, None, R]]) -> Callable[..., None]:
-    @event_loop(close=True)
-    @wraps(f)
-    def wrapper(*args: Any, **kwargs: Any) -> None:
-        asyncio.get_event_loop().run_until_complete(f(*args, **kwargs))
+class FakeParameter(click.Parameter):
+    """A fake click Parameter for when calling functions that need it."""

 
 

-    return wrapper
+    def __init__(self) -> None:
+        pass

 
 
 class BlackRunner(CliRunner):
 
 
 class BlackRunner(CliRunner):


@@ -136,36 +123,24 @@ class BlackRunner(CliRunner):
                 sys.stderr = hold_stderr
 
 
                 sys.stderr = hold_stderr
 
 

-class BlackTestCase(unittest.TestCase):
-    maxDiff = None
-
-    def assertFormatEqual(self, expected: str, actual: str) -> None:
-        if actual != expected and not os.environ.get("SKIP_AST_PRINT"):
-            bdv: black.DebugVisitor[Any]
-            black.out("Expected tree:", fg="green")
-            try:
-                exp_node = black.lib2to3_parse(expected)
-                bdv = black.DebugVisitor()
-                list(bdv.visit(exp_node))
-            except Exception as ve:
-                black.err(str(ve))
-            black.out("Actual tree:", fg="red")
-            try:
-                exp_node = black.lib2to3_parse(actual)
-                bdv = black.DebugVisitor()
-                list(bdv.visit(exp_node))
-            except Exception as ve:
-                black.err(str(ve))
-        self.assertEqual(expected, actual)
-
+class BlackTestCase(BlackBaseTestCase):

     def invokeBlack(
         self, args: List[str], exit_code: int = 0, ignore_config: bool = True
     ) -> None:
         runner = BlackRunner()
         if ignore_config:
     def invokeBlack(
         self, args: List[str], exit_code: int = 0, ignore_config: bool = True
     ) -> None:
         runner = BlackRunner()
         if ignore_config:

-            args = ["--config", str(THIS_DIR / "empty.toml"), *args]
+            args = ["--verbose", "--config", str(THIS_DIR / "empty.toml"), *args]

         result = runner.invoke(black.main, args)
         result = runner.invoke(black.main, args)

-        self.assertEqual(result.exit_code, exit_code, msg=runner.stderr_bytes.decode())
+        self.assertEqual(
+            result.exit_code,
+            exit_code,
+            msg=(
+                f"Failed with args: {args}\n"
+                f"stdout: {runner.stdout_bytes.decode()!r}\n"
+                f"stderr: {runner.stderr_bytes.decode()!r}\n"
+                f"exception: {result.exception}"
+            ),
+        )

 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_empty(self) -> None:
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_empty(self) -> None:


@@ -173,7 +148,7 @@ class BlackTestCase(unittest.TestCase):
         actual = fs(source)
         self.assertFormatEqual(expected, actual)
         black.assert_equivalent(source, actual)
         actual = fs(source)
         self.assertFormatEqual(expected, actual)
         black.assert_equivalent(source, actual)

-        black.assert_stable(source, actual, black.FileMode())
+        black.assert_stable(source, actual, DEFAULT_MODE)

 
     def test_empty_ff(self) -> None:
         expected = ""
 
     def test_empty_ff(self) -> None:
         expected = ""


@@ -186,26 +161,8 @@ class BlackTestCase(unittest.TestCase):
             os.unlink(tmp_file)
         self.assertFormatEqual(expected, actual)
 
             os.unlink(tmp_file)
         self.assertFormatEqual(expected, actual)
 

-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_self(self) -> None:
-        source, expected = read_data("test_black", data=False)
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
-        self.assertFalse(ff(THIS_FILE))
-
-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_black(self) -> None:
-        source, expected = read_data("../black", data=False)
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
-        self.assertFalse(ff(THIS_DIR / ".." / "black.py"))
-

     def test_piping(self) -> None:
     def test_piping(self) -> None:

-        source, expected = read_data("../black", data=False)
+        source, expected = read_data("src/black/__init__", data=False)

         result = BlackRunner().invoke(
             black.main,
             ["-", "--fast", f"--line-length={black.DEFAULT_LINE_LENGTH}"],
         result = BlackRunner().invoke(
             black.main,
             ["-", "--fast", f"--line-length={black.DEFAULT_LINE_LENGTH}"],


@@ -214,12 +171,12 @@ class BlackTestCase(unittest.TestCase):
         self.assertEqual(result.exit_code, 0)
         self.assertFormatEqual(expected, result.output)
         black.assert_equivalent(source, result.output)
         self.assertEqual(result.exit_code, 0)
         self.assertFormatEqual(expected, result.output)
         black.assert_equivalent(source, result.output)

-        black.assert_stable(source, result.output, black.FileMode())
+        black.assert_stable(source, result.output, DEFAULT_MODE)

 
     def test_piping_diff(self) -> None:
         diff_header = re.compile(
 
     def test_piping_diff(self) -> None:
         diff_header = re.compile(

-            rf"(STDIN|STDOUT)\t\d\d\d\d-\d\d-\d\d "
-            rf"\d\d:\d\d:\d\d\.\d\d\d\d\d\d \+\d\d\d\d"
+            r"(STDIN|STDOUT)\t\d\d\d\d-\d\d-\d\d \d\d:\d\d:\d\d\.\d\d\d\d\d\d "
+            r"\+\d\d\d\d"

         )
         source, _ = read_data("expression.py")
         expected, _ = read_data("expression.diff")
         )
         source, _ = read_data("expression.py")
         expected, _ = read_data("expression.diff")


@@ -235,42 +192,93 @@ class BlackTestCase(unittest.TestCase):
             black.main, args, input=BytesIO(source.encode("utf8"))
         )
         self.assertEqual(result.exit_code, 0)
             black.main, args, input=BytesIO(source.encode("utf8"))
         )
         self.assertEqual(result.exit_code, 0)

-        actual = diff_header.sub("[Deterministic header]", result.output)
+        actual = diff_header.sub(DETERMINISTIC_HEADER, result.output)

         actual = actual.rstrip() + "\n"  # the diff output has a trailing space
         self.assertEqual(expected, actual)
 
         actual = actual.rstrip() + "\n"  # the diff output has a trailing space
         self.assertEqual(expected, actual)
 

+    def test_piping_diff_with_color(self) -> None:
+        source, _ = read_data("expression.py")
+        config = THIS_DIR / "data" / "empty_pyproject.toml"
+        args = [
+            "-",
+            "--fast",
+            f"--line-length={black.DEFAULT_LINE_LENGTH}",
+            "--diff",
+            "--color",
+            f"--config={config}",
+        ]
+        result = BlackRunner().invoke(
+            black.main, args, input=BytesIO(source.encode("utf8"))
+        )
+        actual = result.output
+        # Again, the contents are checked in a different test, so only look for colors.
+        self.assertIn("\033[1;37m", actual)
+        self.assertIn("\033[36m", actual)
+        self.assertIn("\033[32m", actual)
+        self.assertIn("\033[31m", actual)
+        self.assertIn("\033[0m", actual)
+

     @patch("black.dump_to_file", dump_to_stderr)
     @patch("black.dump_to_file", dump_to_stderr)

-    def test_setup(self) -> None:
-        source, expected = read_data("../setup", data=False)
-        actual = fs(source)
+    def _test_wip(self) -> None:
+        source, expected = read_data("wip")
+        sys.settrace(tracefunc)
+        mode = replace(
+            DEFAULT_MODE,
+            experimental_string_processing=False,
+            target_versions={black.TargetVersion.PY38},
+        )
+        actual = fs(source, mode=mode)
+        sys.settrace(None)

         self.assertFormatEqual(expected, actual)
         black.assert_equivalent(source, actual)
         black.assert_stable(source, actual, black.FileMode())
         self.assertFormatEqual(expected, actual)
         black.assert_equivalent(source, actual)
         black.assert_stable(source, actual, black.FileMode())

-        self.assertFalse(ff(THIS_DIR / ".." / "setup.py"))

 
 

+    @unittest.expectedFailure

     @patch("black.dump_to_file", dump_to_stderr)
     @patch("black.dump_to_file", dump_to_stderr)

-    def test_function(self) -> None:
-        source, expected = read_data("function")
+    def test_trailing_comma_optional_parens_stability1(self) -> None:
+        source, _expected = read_data("trailing_comma_optional_parens1")

         actual = fs(source)
         actual = fs(source)

-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
+        black.assert_stable(source, actual, DEFAULT_MODE)
+
+    @unittest.expectedFailure
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_trailing_comma_optional_parens_stability2(self) -> None:
+        source, _expected = read_data("trailing_comma_optional_parens2")
+        actual = fs(source)
+        black.assert_stable(source, actual, DEFAULT_MODE)

 
 

+    @unittest.expectedFailure

     @patch("black.dump_to_file", dump_to_stderr)
     @patch("black.dump_to_file", dump_to_stderr)

-    def test_function2(self) -> None:
-        source, expected = read_data("function2")
+    def test_trailing_comma_optional_parens_stability3(self) -> None:
+        source, _expected = read_data("trailing_comma_optional_parens3")
+        actual = fs(source)
+        black.assert_stable(source, actual, DEFAULT_MODE)
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_pep_572(self) -> None:
+        source, expected = read_data("pep_572")

         actual = fs(source)
         self.assertFormatEqual(expected, actual)
         actual = fs(source)
         self.assertFormatEqual(expected, actual)

-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
+        black.assert_stable(source, actual, DEFAULT_MODE)
+        if sys.version_info >= (3, 8):
+            black.assert_equivalent(source, actual)

 
     @patch("black.dump_to_file", dump_to_stderr)
 
     @patch("black.dump_to_file", dump_to_stderr)

-    def test_expression(self) -> None:
-        source, expected = read_data("expression")
+    def test_pep_572_remove_parens(self) -> None:
+        source, expected = read_data("pep_572_remove_parens")

         actual = fs(source)
         self.assertFormatEqual(expected, actual)
         actual = fs(source)
         self.assertFormatEqual(expected, actual)

-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
+        black.assert_stable(source, actual, DEFAULT_MODE)
+        if sys.version_info >= (3, 8):
+            black.assert_equivalent(source, actual)
+
+    def test_pep_572_version_detection(self) -> None:
+        source, _ = read_data("pep_572")
+        root = black.lib2to3_parse(source)
+        features = black.get_features_used(root)
+        self.assertIn(black.Feature.ASSIGNMENT_EXPRESSIONS, features)
+        versions = black.detect_target_versions(root)
+        self.assertIn(black.TargetVersion.PY38, versions)

 
     def test_expression_ff(self) -> None:
         source, expected = read_data("expression")
 
     def test_expression_ff(self) -> None:
         source, expected = read_data("expression")


@@ -284,40 +292,71 @@ class BlackTestCase(unittest.TestCase):
         self.assertFormatEqual(expected, actual)
         with patch("black.dump_to_file", dump_to_stderr):
             black.assert_equivalent(source, actual)
         self.assertFormatEqual(expected, actual)
         with patch("black.dump_to_file", dump_to_stderr):
             black.assert_equivalent(source, actual)

-            black.assert_stable(source, actual, black.FileMode())
+            black.assert_stable(source, actual, DEFAULT_MODE)

 
     def test_expression_diff(self) -> None:
         source, _ = read_data("expression.py")
 
     def test_expression_diff(self) -> None:
         source, _ = read_data("expression.py")

+        config = THIS_DIR / "data" / "empty_pyproject.toml"

         expected, _ = read_data("expression.diff")
         tmp_file = Path(black.dump_to_file(source))
         diff_header = re.compile(
             rf"{re.escape(str(tmp_file))}\t\d\d\d\d-\d\d-\d\d "
         expected, _ = read_data("expression.diff")
         tmp_file = Path(black.dump_to_file(source))
         diff_header = re.compile(
             rf"{re.escape(str(tmp_file))}\t\d\d\d\d-\d\d-\d\d "

-            rf"\d\d:\d\d:\d\d\.\d\d\d\d\d\d \+\d\d\d\d"
+            r"\d\d:\d\d:\d\d\.\d\d\d\d\d\d \+\d\d\d\d"

         )
         try:
         )
         try:

-            result = BlackRunner().invoke(black.main, ["--diff", str(tmp_file)])
+            result = BlackRunner().invoke(
+                black.main, ["--diff", str(tmp_file), f"--config={config}"]
+            )

             self.assertEqual(result.exit_code, 0)
         finally:
             os.unlink(tmp_file)
         actual = result.output
             self.assertEqual(result.exit_code, 0)
         finally:
             os.unlink(tmp_file)
         actual = result.output

-        actual = diff_header.sub("[Deterministic header]", actual)
-        actual = actual.rstrip() + "\n"  # the diff output has a trailing space
+        actual = diff_header.sub(DETERMINISTIC_HEADER, actual)

         if expected != actual:
             dump = black.dump_to_file(actual)
             msg = (
         if expected != actual:
             dump = black.dump_to_file(actual)
             msg = (

-                f"Expected diff isn't equal to the actual. If you made changes "
-                f"to expression.py and this is an anticipated difference, "
-                f"overwrite tests/data/expression.diff with {dump}"
+                "Expected diff isn't equal to the actual. If you made changes to"
+                " expression.py and this is an anticipated difference, overwrite"
+                f" tests/data/expression.diff with {dump}"

             )
             self.assertEqual(expected, actual, msg)
 
             )
             self.assertEqual(expected, actual, msg)
 

+    def test_expression_diff_with_color(self) -> None:
+        source, _ = read_data("expression.py")
+        config = THIS_DIR / "data" / "empty_pyproject.toml"
+        expected, _ = read_data("expression.diff")
+        tmp_file = Path(black.dump_to_file(source))
+        try:
+            result = BlackRunner().invoke(
+                black.main, ["--diff", "--color", str(tmp_file), f"--config={config}"]
+            )
+        finally:
+            os.unlink(tmp_file)
+        actual = result.output
+        # We check the contents of the diff in `test_expression_diff`. All
+        # we need to check here is that color codes exist in the result.
+        self.assertIn("\033[1;37m", actual)
+        self.assertIn("\033[36m", actual)
+        self.assertIn("\033[32m", actual)
+        self.assertIn("\033[31m", actual)
+        self.assertIn("\033[0m", actual)
+

     @patch("black.dump_to_file", dump_to_stderr)
     @patch("black.dump_to_file", dump_to_stderr)

-    def test_fstring(self) -> None:
-        source, expected = read_data("fstring")
+    def test_pep_570(self) -> None:
+        source, expected = read_data("pep_570")

         actual = fs(source)
         self.assertFormatEqual(expected, actual)
         actual = fs(source)
         self.assertFormatEqual(expected, actual)

-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
+        black.assert_stable(source, actual, DEFAULT_MODE)
+        if sys.version_info >= (3, 8):
+            black.assert_equivalent(source, actual)
+
+    def test_detect_pos_only_arguments(self) -> None:
+        source, _ = read_data("pep_570")
+        root = black.lib2to3_parse(source)
+        features = black.get_features_used(root)
+        self.assertIn(black.Feature.POS_ONLY_ARGUMENTS, features)
+        versions = black.detect_target_versions(root)
+        self.assertIn(black.TargetVersion.PY38, versions)

 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_string_quotes(self) -> None:
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_string_quotes(self) -> None:


@@ -325,121 +364,35 @@ class BlackTestCase(unittest.TestCase):
         actual = fs(source)
         self.assertFormatEqual(expected, actual)
         black.assert_equivalent(source, actual)
         actual = fs(source)
         self.assertFormatEqual(expected, actual)
         black.assert_equivalent(source, actual)

-        black.assert_stable(source, actual, black.FileMode())
-        mode = black.FileMode(string_normalization=False)
+        black.assert_stable(source, actual, DEFAULT_MODE)
+        mode = replace(DEFAULT_MODE, string_normalization=False)

         not_normalized = fs(source, mode=mode)
         not_normalized = fs(source, mode=mode)

-        self.assertFormatEqual(source, not_normalized)
+        self.assertFormatEqual(source.replace("\\\n", ""), not_normalized)

         black.assert_equivalent(source, not_normalized)
         black.assert_stable(source, not_normalized, mode=mode)
 
     @patch("black.dump_to_file", dump_to_stderr)
         black.assert_equivalent(source, not_normalized)
         black.assert_stable(source, not_normalized, mode=mode)
 
     @patch("black.dump_to_file", dump_to_stderr)

-    def test_slices(self) -> None:
-        source, expected = read_data("slices")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
-
-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_comments(self) -> None:
-        source, expected = read_data("comments")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
-
-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_comments2(self) -> None:
-        source, expected = read_data("comments2")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
-
-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_comments3(self) -> None:
-        source, expected = read_data("comments3")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
-
-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_comments4(self) -> None:
-        source, expected = read_data("comments4")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
-
-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_comments5(self) -> None:
-        source, expected = read_data("comments5")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
-
-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_comments6(self) -> None:
-        source, expected = read_data("comments6")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
-
-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_comments7(self) -> None:
-        source, expected = read_data("comments7")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
-
-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_cantfit(self) -> None:
-        source, expected = read_data("cantfit")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
-
-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_import_spacing(self) -> None:
-        source, expected = read_data("import_spacing")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
-
-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_composition(self) -> None:
-        source, expected = read_data("composition")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
-
-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_empty_lines(self) -> None:
-        source, expected = read_data("empty_lines")
-        actual = fs(source)
+    def test_docstring_no_string_normalization(self) -> None:
+        """Like test_docstring but with string normalization off."""
+        source, expected = read_data("docstring_no_string_normalization")
+        mode = replace(DEFAULT_MODE, string_normalization=False)
+        actual = fs(source, mode=mode)

         self.assertFormatEqual(expected, actual)
         black.assert_equivalent(source, actual)
         self.assertFormatEqual(expected, actual)
         black.assert_equivalent(source, actual)

-        black.assert_stable(source, actual, black.FileMode())
+        black.assert_stable(source, actual, mode)

 
 

-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_string_prefixes(self) -> None:
-        source, expected = read_data("string_prefixes")
-        actual = fs(source)
+    def test_long_strings_flag_disabled(self) -> None:
+        """Tests for turning off the string processing logic."""
+        source, expected = read_data("long_strings_flag_disabled")
+        mode = replace(DEFAULT_MODE, experimental_string_processing=False)
+        actual = fs(source, mode=mode)

         self.assertFormatEqual(expected, actual)
         self.assertFormatEqual(expected, actual)

-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
+        black.assert_stable(expected, actual, mode)

 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_numeric_literals(self) -> None:
         source, expected = read_data("numeric_literals")
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_numeric_literals(self) -> None:
         source, expected = read_data("numeric_literals")

-        mode = black.FileMode(target_versions=black.PY36_VERSIONS)
+        mode = replace(DEFAULT_MODE, target_versions=PY36_VERSIONS)

         actual = fs(source, mode=mode)
         self.assertFormatEqual(expected, actual)
         black.assert_equivalent(source, actual)
         actual = fs(source, mode=mode)
         self.assertFormatEqual(expected, actual)
         black.assert_equivalent(source, actual)


@@ -448,99 +401,103 @@ class BlackTestCase(unittest.TestCase):
     @patch("black.dump_to_file", dump_to_stderr)
     def test_numeric_literals_ignoring_underscores(self) -> None:
         source, expected = read_data("numeric_literals_skip_underscores")
     @patch("black.dump_to_file", dump_to_stderr)
     def test_numeric_literals_ignoring_underscores(self) -> None:
         source, expected = read_data("numeric_literals_skip_underscores")

-        mode = black.FileMode(target_versions=black.PY36_VERSIONS)
+        mode = replace(DEFAULT_MODE, target_versions=PY36_VERSIONS)

         actual = fs(source, mode=mode)
         self.assertFormatEqual(expected, actual)
         black.assert_equivalent(source, actual)
         black.assert_stable(source, actual, mode)
 
         actual = fs(source, mode=mode)
         self.assertFormatEqual(expected, actual)
         black.assert_equivalent(source, actual)
         black.assert_stable(source, actual, mode)
 

-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_numeric_literals_py2(self) -> None:
-        source, expected = read_data("numeric_literals_py2")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_stable(source, actual, black.FileMode())
-
-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_python2(self) -> None:
-        source, expected = read_data("python2")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        # black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
+    def test_skip_magic_trailing_comma(self) -> None:
+        source, _ = read_data("expression.py")
+        expected, _ = read_data("expression_skip_magic_trailing_comma.diff")
+        tmp_file = Path(black.dump_to_file(source))
+        diff_header = re.compile(
+            rf"{re.escape(str(tmp_file))}\t\d\d\d\d-\d\d-\d\d "
+            r"\d\d:\d\d:\d\d\.\d\d\d\d\d\d \+\d\d\d\d"
+        )
+        try:
+            result = BlackRunner().invoke(black.main, ["-C", "--diff", str(tmp_file)])
+            self.assertEqual(result.exit_code, 0)
+        finally:
+            os.unlink(tmp_file)
+        actual = result.output
+        actual = diff_header.sub(DETERMINISTIC_HEADER, actual)
+        actual = actual.rstrip() + "\n"  # the diff output has a trailing space
+        if expected != actual:
+            dump = black.dump_to_file(actual)
+            msg = (
+                "Expected diff isn't equal to the actual. If you made changes to"
+                " expression.py and this is an anticipated difference, overwrite"
+                f" tests/data/expression_skip_magic_trailing_comma.diff with {dump}"
+            )
+            self.assertEqual(expected, actual, msg)

 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_python2_print_function(self) -> None:
         source, expected = read_data("python2_print_function")
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_python2_print_function(self) -> None:
         source, expected = read_data("python2_print_function")

-        mode = black.FileMode(target_versions={TargetVersion.PY27})
+        mode = replace(DEFAULT_MODE, target_versions={TargetVersion.PY27})

         actual = fs(source, mode=mode)
         self.assertFormatEqual(expected, actual)
         actual = fs(source, mode=mode)
         self.assertFormatEqual(expected, actual)

+        black.assert_equivalent(source, actual)

         black.assert_stable(source, actual, mode)
 
         black.assert_stable(source, actual, mode)
 

-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_python2_unicode_literals(self) -> None:
-        source, expected = read_data("python2_unicode_literals")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_stable(source, actual, black.FileMode())
-

     @patch("black.dump_to_file", dump_to_stderr)
     def test_stub(self) -> None:
     @patch("black.dump_to_file", dump_to_stderr)
     def test_stub(self) -> None:

-        mode = black.FileMode(is_pyi=True)
+        mode = replace(DEFAULT_MODE, is_pyi=True)

         source, expected = read_data("stub.pyi")
         actual = fs(source, mode=mode)
         self.assertFormatEqual(expected, actual)
         black.assert_stable(source, actual, mode)
 
     @patch("black.dump_to_file", dump_to_stderr)
         source, expected = read_data("stub.pyi")
         actual = fs(source, mode=mode)
         self.assertFormatEqual(expected, actual)
         black.assert_stable(source, actual, mode)
 
     @patch("black.dump_to_file", dump_to_stderr)

-    def test_python37(self) -> None:
-        source, expected = read_data("python37")
+    def test_async_as_identifier(self) -> None:
+        source_path = (THIS_DIR / "data" / "async_as_identifier.py").resolve()
+        source, expected = read_data("async_as_identifier")

         actual = fs(source)
         self.assertFormatEqual(expected, actual)
         major, minor = sys.version_info[:2]
         actual = fs(source)
         self.assertFormatEqual(expected, actual)
         major, minor = sys.version_info[:2]

-        if major > 3 or (major == 3 and minor >= 7):
+        if major < 3 or (major <= 3 and minor < 7):

             black.assert_equivalent(source, actual)
             black.assert_equivalent(source, actual)

-        black.assert_stable(source, actual, black.FileMode())
+        black.assert_stable(source, actual, DEFAULT_MODE)
+        # ensure black can parse this when the target is 3.6
+        self.invokeBlack([str(source_path), "--target-version", "py36"])
+        # but not on 3.7, because async/await is no longer an identifier
+        self.invokeBlack([str(source_path), "--target-version", "py37"], exit_code=123)

 
     @patch("black.dump_to_file", dump_to_stderr)
 
     @patch("black.dump_to_file", dump_to_stderr)

-    def test_fmtonoff(self) -> None:
-        source, expected = read_data("fmtonoff")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
-
-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_fmtonoff2(self) -> None:
-        source, expected = read_data("fmtonoff2")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
-
-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_remove_empty_parentheses_after_class(self) -> None:
-        source, expected = read_data("class_blank_parentheses")
+    def test_python37(self) -> None:
+        source_path = (THIS_DIR / "data" / "python37.py").resolve()
+        source, expected = read_data("python37")

         actual = fs(source)
         self.assertFormatEqual(expected, actual)
         actual = fs(source)
         self.assertFormatEqual(expected, actual)

-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
+        major, minor = sys.version_info[:2]
+        if major > 3 or (major == 3 and minor >= 7):
+            black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, DEFAULT_MODE)
+        # ensure black can parse this when the target is 3.7
+        self.invokeBlack([str(source_path), "--target-version", "py37"])
+        # but not on 3.6, because we use async as a reserved keyword
+        self.invokeBlack([str(source_path), "--target-version", "py36"], exit_code=123)

 
     @patch("black.dump_to_file", dump_to_stderr)
 
     @patch("black.dump_to_file", dump_to_stderr)

-    def test_new_line_between_class_and_code(self) -> None:
-        source, expected = read_data("class_methods_new_line")
+    def test_python38(self) -> None:
+        source, expected = read_data("python38")

         actual = fs(source)
         self.assertFormatEqual(expected, actual)
         actual = fs(source)
         self.assertFormatEqual(expected, actual)

-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
+        major, minor = sys.version_info[:2]
+        if major > 3 or (major == 3 and minor >= 8):
+            black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, DEFAULT_MODE)

 
     @patch("black.dump_to_file", dump_to_stderr)
 
     @patch("black.dump_to_file", dump_to_stderr)

-    def test_bracket_match(self) -> None:
-        source, expected = read_data("bracketmatch")
+    def test_python39(self) -> None:
+        source, expected = read_data("python39")

         actual = fs(source)
         self.assertFormatEqual(expected, actual)
         actual = fs(source)
         self.assertFormatEqual(expected, actual)

-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, black.FileMode())
+        major, minor = sys.version_info[:2]
+        if major > 3 or (major == 3 and minor >= 9):
+            black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, DEFAULT_MODE)

 
     def test_tab_comment_indentation(self) -> None:
         contents_tab = "if 1:\n\tif 2:\n\t\tpass\n\t# comment\n\tpass\n"
 
     def test_tab_comment_indentation(self) -> None:
         contents_tab = "if 1:\n\tif 2:\n\t\tpass\n\t# comment\n\tpass\n"


@@ -608,8 +565,8 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(err_lines[-1], "error: cannot format e1: boom")
             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(err_lines[-1], "error: cannot format e1: boom")
             self.assertEqual(
                 unstyle(str(report)),

-                "1 file reformatted, 2 files left unchanged, "
-                "1 file failed to reformat.",
+                "1 file reformatted, 2 files left unchanged, 1 file failed to"
+                " reformat.",

             )
             self.assertEqual(report.return_code, 123)
             report.done(Path("f3"), black.Changed.YES)
             )
             self.assertEqual(report.return_code, 123)
             report.done(Path("f3"), black.Changed.YES)


@@ -618,8 +575,8 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(out_lines[-1], "reformatted f3")
             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(out_lines[-1], "reformatted f3")
             self.assertEqual(
                 unstyle(str(report)),

-                "2 files reformatted, 2 files left unchanged, "
-                "1 file failed to reformat.",
+                "2 files reformatted, 2 files left unchanged, 1 file failed to"
+                " reformat.",

             )
             self.assertEqual(report.return_code, 123)
             report.failed(Path("e2"), "boom")
             )
             self.assertEqual(report.return_code, 123)
             report.failed(Path("e2"), "boom")


@@ -628,8 +585,8 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(err_lines[-1], "error: cannot format e2: boom")
             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(err_lines[-1], "error: cannot format e2: boom")
             self.assertEqual(
                 unstyle(str(report)),

-                "2 files reformatted, 2 files left unchanged, "
-                "2 files failed to reformat.",
+                "2 files reformatted, 2 files left unchanged, 2 files failed to"
+                " reformat.",

             )
             self.assertEqual(report.return_code, 123)
             report.path_ignored(Path("wat"), "no match")
             )
             self.assertEqual(report.return_code, 123)
             report.path_ignored(Path("wat"), "no match")


@@ -638,8 +595,8 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(out_lines[-1], "wat ignored: no match")
             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(out_lines[-1], "wat ignored: no match")
             self.assertEqual(
                 unstyle(str(report)),

-                "2 files reformatted, 2 files left unchanged, "
-                "2 files failed to reformat.",
+                "2 files reformatted, 2 files left unchanged, 2 files failed to"
+                " reformat.",

             )
             self.assertEqual(report.return_code, 123)
             report.done(Path("f4"), black.Changed.NO)
             )
             self.assertEqual(report.return_code, 123)
             report.done(Path("f4"), black.Changed.NO)


@@ -648,15 +605,22 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(out_lines[-1], "f4 already well formatted, good job.")
             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(out_lines[-1], "f4 already well formatted, good job.")
             self.assertEqual(
                 unstyle(str(report)),

-                "2 files reformatted, 3 files left unchanged, "
-                "2 files failed to reformat.",
+                "2 files reformatted, 3 files left unchanged, 2 files failed to"
+                " reformat.",

             )
             self.assertEqual(report.return_code, 123)
             report.check = True
             self.assertEqual(
                 unstyle(str(report)),
             )
             self.assertEqual(report.return_code, 123)
             report.check = True
             self.assertEqual(
                 unstyle(str(report)),

-                "2 files would be reformatted, 3 files would be left unchanged, "
-                "2 files would fail to reformat.",
+                "2 files would be reformatted, 3 files would be left unchanged, 2 files"
+                " would fail to reformat.",
+            )
+            report.check = False
+            report.diff = True
+            self.assertEqual(
+                unstyle(str(report)),
+                "2 files would be reformatted, 3 files would be left unchanged, 2 files"
+                " would fail to reformat.",

             )
 
     def test_report_quiet(self) -> None:
             )
 
     def test_report_quiet(self) -> None:


@@ -698,8 +662,8 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(err_lines[-1], "error: cannot format e1: boom")
             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(err_lines[-1], "error: cannot format e1: boom")
             self.assertEqual(
                 unstyle(str(report)),

-                "1 file reformatted, 2 files left unchanged, "
-                "1 file failed to reformat.",
+                "1 file reformatted, 2 files left unchanged, 1 file failed to"
+                " reformat.",

             )
             self.assertEqual(report.return_code, 123)
             report.done(Path("f3"), black.Changed.YES)
             )
             self.assertEqual(report.return_code, 123)
             report.done(Path("f3"), black.Changed.YES)


@@ -707,8 +671,8 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(len(err_lines), 1)
             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(len(err_lines), 1)
             self.assertEqual(
                 unstyle(str(report)),

-                "2 files reformatted, 2 files left unchanged, "
-                "1 file failed to reformat.",
+                "2 files reformatted, 2 files left unchanged, 1 file failed to"
+                " reformat.",

             )
             self.assertEqual(report.return_code, 123)
             report.failed(Path("e2"), "boom")
             )
             self.assertEqual(report.return_code, 123)
             report.failed(Path("e2"), "boom")


@@ -717,8 +681,8 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(err_lines[-1], "error: cannot format e2: boom")
             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(err_lines[-1], "error: cannot format e2: boom")
             self.assertEqual(
                 unstyle(str(report)),

-                "2 files reformatted, 2 files left unchanged, "
-                "2 files failed to reformat.",
+                "2 files reformatted, 2 files left unchanged, 2 files failed to"
+                " reformat.",

             )
             self.assertEqual(report.return_code, 123)
             report.path_ignored(Path("wat"), "no match")
             )
             self.assertEqual(report.return_code, 123)
             report.path_ignored(Path("wat"), "no match")


@@ -726,8 +690,8 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(len(err_lines), 2)
             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(len(err_lines), 2)
             self.assertEqual(
                 unstyle(str(report)),

-                "2 files reformatted, 2 files left unchanged, "
-                "2 files failed to reformat.",
+                "2 files reformatted, 2 files left unchanged, 2 files failed to"
+                " reformat.",

             )
             self.assertEqual(report.return_code, 123)
             report.done(Path("f4"), black.Changed.NO)
             )
             self.assertEqual(report.return_code, 123)
             report.done(Path("f4"), black.Changed.NO)


@@ -735,15 +699,22 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(len(err_lines), 2)
             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(len(err_lines), 2)
             self.assertEqual(
                 unstyle(str(report)),

-                "2 files reformatted, 3 files left unchanged, "
-                "2 files failed to reformat.",
+                "2 files reformatted, 3 files left unchanged, 2 files failed to"
+                " reformat.",

             )
             self.assertEqual(report.return_code, 123)
             report.check = True
             self.assertEqual(
                 unstyle(str(report)),
             )
             self.assertEqual(report.return_code, 123)
             report.check = True
             self.assertEqual(
                 unstyle(str(report)),

-                "2 files would be reformatted, 3 files would be left unchanged, "
-                "2 files would fail to reformat.",
+                "2 files would be reformatted, 3 files would be left unchanged, 2 files"
+                " would fail to reformat.",
+            )
+            report.check = False
+            report.diff = True
+            self.assertEqual(
+                unstyle(str(report)),
+                "2 files would be reformatted, 3 files would be left unchanged, 2 files"
+                " would fail to reformat.",

             )
 
     def test_report_normal(self) -> None:
             )
 
     def test_report_normal(self) -> None:


@@ -787,8 +758,8 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(err_lines[-1], "error: cannot format e1: boom")
             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(err_lines[-1], "error: cannot format e1: boom")
             self.assertEqual(
                 unstyle(str(report)),

-                "1 file reformatted, 2 files left unchanged, "
-                "1 file failed to reformat.",
+                "1 file reformatted, 2 files left unchanged, 1 file failed to"
+                " reformat.",

             )
             self.assertEqual(report.return_code, 123)
             report.done(Path("f3"), black.Changed.YES)
             )
             self.assertEqual(report.return_code, 123)
             report.done(Path("f3"), black.Changed.YES)


@@ -797,8 +768,8 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(out_lines[-1], "reformatted f3")
             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(out_lines[-1], "reformatted f3")
             self.assertEqual(
                 unstyle(str(report)),

-                "2 files reformatted, 2 files left unchanged, "
-                "1 file failed to reformat.",
+                "2 files reformatted, 2 files left unchanged, 1 file failed to"
+                " reformat.",

             )
             self.assertEqual(report.return_code, 123)
             report.failed(Path("e2"), "boom")
             )
             self.assertEqual(report.return_code, 123)
             report.failed(Path("e2"), "boom")


@@ -807,8 +778,8 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(err_lines[-1], "error: cannot format e2: boom")
             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(err_lines[-1], "error: cannot format e2: boom")
             self.assertEqual(
                 unstyle(str(report)),

-                "2 files reformatted, 2 files left unchanged, "
-                "2 files failed to reformat.",
+                "2 files reformatted, 2 files left unchanged, 2 files failed to"
+                " reformat.",

             )
             self.assertEqual(report.return_code, 123)
             report.path_ignored(Path("wat"), "no match")
             )
             self.assertEqual(report.return_code, 123)
             report.path_ignored(Path("wat"), "no match")


@@ -816,8 +787,8 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(len(err_lines), 2)
             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(len(err_lines), 2)
             self.assertEqual(
                 unstyle(str(report)),

-                "2 files reformatted, 2 files left unchanged, "
-                "2 files failed to reformat.",
+                "2 files reformatted, 2 files left unchanged, 2 files failed to"
+                " reformat.",

             )
             self.assertEqual(report.return_code, 123)
             report.done(Path("f4"), black.Changed.NO)
             )
             self.assertEqual(report.return_code, 123)
             report.done(Path("f4"), black.Changed.NO)


@@ -825,15 +796,22 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(len(err_lines), 2)
             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(len(err_lines), 2)
             self.assertEqual(
                 unstyle(str(report)),

-                "2 files reformatted, 3 files left unchanged, "
-                "2 files failed to reformat.",
+                "2 files reformatted, 3 files left unchanged, 2 files failed to"
+                " reformat.",

             )
             self.assertEqual(report.return_code, 123)
             report.check = True
             self.assertEqual(
                 unstyle(str(report)),
             )
             self.assertEqual(report.return_code, 123)
             report.check = True
             self.assertEqual(
                 unstyle(str(report)),

-                "2 files would be reformatted, 3 files would be left unchanged, "
-                "2 files would fail to reformat.",
+                "2 files would be reformatted, 3 files would be left unchanged, 2 files"
+                " would fail to reformat.",
+            )
+            report.check = False
+            report.diff = True
+            self.assertEqual(
+                unstyle(str(report)),
+                "2 files would be reformatted, 3 files would be left unchanged, 2 files"
+                " would fail to reformat.",

             )
 
     def test_lib2to3_parse(self) -> None:
             )
 
     def test_lib2to3_parse(self) -> None:


@@ -861,6 +839,39 @@ class BlackTestCase(unittest.TestCase):
         black.lib2to3_parse(py3_only, {TargetVersion.PY36})
         black.lib2to3_parse(py3_only, {TargetVersion.PY27, TargetVersion.PY36})
 
         black.lib2to3_parse(py3_only, {TargetVersion.PY36})
         black.lib2to3_parse(py3_only, {TargetVersion.PY27, TargetVersion.PY36})
 

+    def test_get_features_used_decorator(self) -> None:
+        # Test the feature detection of new decorator syntax
+        # since this makes some test cases of test_get_features_used()
+        # fails if it fails, this is tested first so that a useful case
+        # is identified
+        simples, relaxed = read_data("decorators")
+        # skip explanation comments at the top of the file
+        for simple_test in simples.split("##")[1:]:
+            node = black.lib2to3_parse(simple_test)
+            decorator = str(node.children[0].children[0]).strip()
+            self.assertNotIn(
+                Feature.RELAXED_DECORATORS,
+                black.get_features_used(node),
+                msg=(
+                    f"decorator '{decorator}' follows python<=3.8 syntax"
+                    "but is detected as 3.9+"
+                    # f"The full node is\n{node!r}"
+                ),
+            )
+        # skip the '# output' comment at the top of the output part
+        for relaxed_test in relaxed.split("##")[1:]:
+            node = black.lib2to3_parse(relaxed_test)
+            decorator = str(node.children[0].children[0]).strip()
+            self.assertIn(
+                Feature.RELAXED_DECORATORS,
+                black.get_features_used(node),
+                msg=(
+                    f"decorator '{decorator}' uses python3.9+ syntax"
+                    "but is detected as python<=3.8"
+                    # f"The full node is\n{node!r}"
+                ),
+            )
+

     def test_get_features_used(self) -> None:
         node = black.lib2to3_parse("def f(*, arg): ...\n")
         self.assertEqual(black.get_features_used(node), set())
     def test_get_features_used(self) -> None:
         node = black.lib2to3_parse("def f(*, arg): ...\n")
         self.assertEqual(black.get_features_used(node), set())


@@ -948,16 +959,16 @@ class BlackTestCase(unittest.TestCase):
 
     def test_format_file_contents(self) -> None:
         empty = ""
 
     def test_format_file_contents(self) -> None:
         empty = ""

-        mode = black.FileMode()
+        mode = DEFAULT_MODE

         with self.assertRaises(black.NothingChanged):
             black.format_file_contents(empty, mode=mode, fast=False)
         just_nl = "\n"
         with self.assertRaises(black.NothingChanged):
             black.format_file_contents(just_nl, mode=mode, fast=False)
         with self.assertRaises(black.NothingChanged):
             black.format_file_contents(empty, mode=mode, fast=False)
         just_nl = "\n"
         with self.assertRaises(black.NothingChanged):
             black.format_file_contents(just_nl, mode=mode, fast=False)

-        same = "l = [1, 2, 3]\n"
+        same = "j = [1, 2, 3]\n"

         with self.assertRaises(black.NothingChanged):
             black.format_file_contents(same, mode=mode, fast=False)
         with self.assertRaises(black.NothingChanged):
             black.format_file_contents(same, mode=mode, fast=False)

-        different = "l = [1,2,3]"
+        different = "j = [1,2,3]"

         expected = same
         actual = black.format_file_contents(different, mode=mode, fast=False)
         self.assertEqual(expected, actual)
         expected = same
         actual = black.format_file_contents(different, mode=mode, fast=False)
         self.assertEqual(expected, actual)


@@ -985,7 +996,7 @@ class BlackTestCase(unittest.TestCase):
 
         with patch("black.out", out), patch("black.err", err):
             with self.assertRaises(AssertionError):
 
         with patch("black.out", out), patch("black.err", err):
             with self.assertRaises(AssertionError):

-                self.assertFormatEqual("l = [1, 2, 3]", "l = [1, 2, 3,]")
+                self.assertFormatEqual("j = [1, 2, 3]", "j = [1, 2, 3,]")

 
         out_str = "".join(out_lines)
         self.assertTrue("Expected tree:" in out_str)
 
         out_str = "".join(out_lines)
         self.assertTrue("Expected tree:" in out_str)


@@ -993,7 +1004,7 @@ class BlackTestCase(unittest.TestCase):
         self.assertEqual("".join(err_lines), "")
 
     def test_cache_broken_file(self) -> None:
         self.assertEqual("".join(err_lines), "")
 
     def test_cache_broken_file(self) -> None:

-        mode = black.FileMode()
+        mode = DEFAULT_MODE

         with cache_dir() as workspace:
             cache_file = black.get_cache_file(mode)
             with cache_file.open("w") as fobj:
         with cache_dir() as workspace:
             cache_file = black.get_cache_file(mode)
             with cache_file.open("w") as fobj:


@@ -1004,10 +1015,10 @@ class BlackTestCase(unittest.TestCase):
                 fobj.write("print('hello')")
             self.invokeBlack([str(src)])
             cache = black.read_cache(mode)
                 fobj.write("print('hello')")
             self.invokeBlack([str(src)])
             cache = black.read_cache(mode)

-            self.assertIn(src, cache)
+            self.assertIn(str(src), cache)

 
     def test_cache_single_file_already_cached(self) -> None:
 
     def test_cache_single_file_already_cached(self) -> None:

-        mode = black.FileMode()
+        mode = DEFAULT_MODE

         with cache_dir() as workspace:
             src = (workspace / "test.py").resolve()
             with src.open("w") as fobj:
         with cache_dir() as workspace:
             src = (workspace / "test.py").resolve()
             with src.open("w") as fobj:


@@ -1017,9 +1028,9 @@ class BlackTestCase(unittest.TestCase):
             with src.open("r") as fobj:
                 self.assertEqual(fobj.read(), "print('hello')")
 
             with src.open("r") as fobj:
                 self.assertEqual(fobj.read(), "print('hello')")
 

-    @event_loop(close=False)
+    @event_loop()

     def test_cache_multiple_files(self) -> None:
     def test_cache_multiple_files(self) -> None:

-        mode = black.FileMode()
+        mode = DEFAULT_MODE

         with cache_dir() as workspace, patch(
             "black.ProcessPoolExecutor", new=ThreadPoolExecutor
         ):
         with cache_dir() as workspace, patch(
             "black.ProcessPoolExecutor", new=ThreadPoolExecutor
         ):


@@ -1036,21 +1047,67 @@ class BlackTestCase(unittest.TestCase):
             with two.open("r") as fobj:
                 self.assertEqual(fobj.read(), 'print("hello")\n')
             cache = black.read_cache(mode)
             with two.open("r") as fobj:
                 self.assertEqual(fobj.read(), 'print("hello")\n')
             cache = black.read_cache(mode)

-            self.assertIn(one, cache)
-            self.assertIn(two, cache)
+            self.assertIn(str(one), cache)
+            self.assertIn(str(two), cache)

 
     def test_no_cache_when_writeback_diff(self) -> None:
 
     def test_no_cache_when_writeback_diff(self) -> None:

-        mode = black.FileMode()
+        mode = DEFAULT_MODE

         with cache_dir() as workspace:
             src = (workspace / "test.py").resolve()
             with src.open("w") as fobj:
                 fobj.write("print('hello')")
         with cache_dir() as workspace:
             src = (workspace / "test.py").resolve()
             with src.open("w") as fobj:
                 fobj.write("print('hello')")

-            self.invokeBlack([str(src), "--diff"])
-            cache_file = black.get_cache_file(mode)
-            self.assertFalse(cache_file.exists())
+            with patch("black.read_cache") as read_cache, patch(
+                "black.write_cache"
+            ) as write_cache:
+                self.invokeBlack([str(src), "--diff"])
+                cache_file = black.get_cache_file(mode)
+                self.assertFalse(cache_file.exists())
+                write_cache.assert_not_called()
+                read_cache.assert_not_called()
+
+    def test_no_cache_when_writeback_color_diff(self) -> None:
+        mode = DEFAULT_MODE
+        with cache_dir() as workspace:
+            src = (workspace / "test.py").resolve()
+            with src.open("w") as fobj:
+                fobj.write("print('hello')")
+            with patch("black.read_cache") as read_cache, patch(
+                "black.write_cache"
+            ) as write_cache:
+                self.invokeBlack([str(src), "--diff", "--color"])
+                cache_file = black.get_cache_file(mode)
+                self.assertFalse(cache_file.exists())
+                write_cache.assert_not_called()
+                read_cache.assert_not_called()
+
+    @event_loop()
+    def test_output_locking_when_writeback_diff(self) -> None:
+        with cache_dir() as workspace:
+            for tag in range(0, 4):
+                src = (workspace / f"test{tag}.py").resolve()
+                with src.open("w") as fobj:
+                    fobj.write("print('hello')")
+            with patch("black.Manager", wraps=multiprocessing.Manager) as mgr:
+                self.invokeBlack(["--diff", str(workspace)], exit_code=0)
+                # this isn't quite doing what we want, but if it _isn't_
+                # called then we cannot be using the lock it provides
+                mgr.assert_called()
+
+    @event_loop()
+    def test_output_locking_when_writeback_color_diff(self) -> None:
+        with cache_dir() as workspace:
+            for tag in range(0, 4):
+                src = (workspace / f"test{tag}.py").resolve()
+                with src.open("w") as fobj:
+                    fobj.write("print('hello')")
+            with patch("black.Manager", wraps=multiprocessing.Manager) as mgr:
+                self.invokeBlack(["--diff", "--color", str(workspace)], exit_code=0)
+                # this isn't quite doing what we want, but if it _isn't_
+                # called then we cannot be using the lock it provides
+                mgr.assert_called()

 
     def test_no_cache_when_stdin(self) -> None:
 
     def test_no_cache_when_stdin(self) -> None:

-        mode = black.FileMode()
+        mode = DEFAULT_MODE

         with cache_dir():
             result = CliRunner().invoke(
                 black.main, ["-"], input=BytesIO(b"print('hello')")
         with cache_dir():
             result = CliRunner().invoke(
                 black.main, ["-"], input=BytesIO(b"print('hello')")


@@ -1060,19 +1117,19 @@ class BlackTestCase(unittest.TestCase):
             self.assertFalse(cache_file.exists())
 
     def test_read_cache_no_cachefile(self) -> None:
             self.assertFalse(cache_file.exists())
 
     def test_read_cache_no_cachefile(self) -> None:

-        mode = black.FileMode()
+        mode = DEFAULT_MODE

         with cache_dir():
             self.assertEqual(black.read_cache(mode), {})
 
     def test_write_cache_read_cache(self) -> None:
         with cache_dir():
             self.assertEqual(black.read_cache(mode), {})
 
     def test_write_cache_read_cache(self) -> None:

-        mode = black.FileMode()
+        mode = DEFAULT_MODE

         with cache_dir() as workspace:
             src = (workspace / "test.py").resolve()
             src.touch()
             black.write_cache({}, [src], mode)
             cache = black.read_cache(mode)
         with cache_dir() as workspace:
             src = (workspace / "test.py").resolve()
             src.touch()
             black.write_cache({}, [src], mode)
             cache = black.read_cache(mode)

-            self.assertIn(src, cache)
-            self.assertEqual(cache[src], black.get_cache_info(src))
+            self.assertIn(str(src), cache)
+            self.assertEqual(cache[str(src)], black.get_cache_info(src))

 
     def test_filter_cached(self) -> None:
         with TemporaryDirectory() as workspace:
 
     def test_filter_cached(self) -> None:
         with TemporaryDirectory() as workspace:


@@ -1083,7 +1140,10 @@ class BlackTestCase(unittest.TestCase):
             uncached.touch()
             cached.touch()
             cached_but_changed.touch()
             uncached.touch()
             cached.touch()
             cached_but_changed.touch()

-            cache = {cached: black.get_cache_info(cached), cached_but_changed: (0.0, 0)}
+            cache = {
+                str(cached): black.get_cache_info(cached),
+                str(cached_but_changed): (0.0, 0),
+            }

             todo, done = black.filter_cached(
                 cache, {uncached, cached, cached_but_changed}
             )
             todo, done = black.filter_cached(
                 cache, {uncached, cached, cached_but_changed}
             )


@@ -1091,15 +1151,15 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(done, {cached})
 
     def test_write_cache_creates_directory_if_needed(self) -> None:
             self.assertEqual(done, {cached})
 
     def test_write_cache_creates_directory_if_needed(self) -> None:

-        mode = black.FileMode()
+        mode = DEFAULT_MODE

         with cache_dir(exists=False) as workspace:
             self.assertFalse(workspace.exists())
             black.write_cache({}, [], mode)
             self.assertTrue(workspace.exists())
 
         with cache_dir(exists=False) as workspace:
             self.assertFalse(workspace.exists())
             black.write_cache({}, [], mode)
             self.assertTrue(workspace.exists())
 

-    @event_loop(close=False)
+    @event_loop()

     def test_failed_formatting_does_not_get_cached(self) -> None:
     def test_failed_formatting_does_not_get_cached(self) -> None:

-        mode = black.FileMode()
+        mode = DEFAULT_MODE

         with cache_dir() as workspace, patch(
             "black.ProcessPoolExecutor", new=ThreadPoolExecutor
         ):
         with cache_dir() as workspace, patch(
             "black.ProcessPoolExecutor", new=ThreadPoolExecutor
         ):


@@ -1111,16 +1171,27 @@ class BlackTestCase(unittest.TestCase):
                 fobj.write('print("hello")\n')
             self.invokeBlack([str(workspace)], exit_code=123)
             cache = black.read_cache(mode)
                 fobj.write('print("hello")\n')
             self.invokeBlack([str(workspace)], exit_code=123)
             cache = black.read_cache(mode)

-            self.assertNotIn(failing, cache)
-            self.assertIn(clean, cache)
+            self.assertNotIn(str(failing), cache)
+            self.assertIn(str(clean), cache)

 
     def test_write_cache_write_fail(self) -> None:
 
     def test_write_cache_write_fail(self) -> None:

-        mode = black.FileMode()
+        mode = DEFAULT_MODE

         with cache_dir(), patch.object(Path, "open") as mock:
             mock.side_effect = OSError
             black.write_cache({}, [], mode)
 
         with cache_dir(), patch.object(Path, "open") as mock:
             mock.side_effect = OSError
             black.write_cache({}, [], mode)
 

-    @event_loop(close=False)
+    @event_loop()
+    @patch("black.ProcessPoolExecutor", MagicMock(side_effect=OSError))
+    def test_works_in_mono_process_only_environment(self) -> None:
+        with cache_dir() as workspace:
+            for f in [
+                (workspace / "one.py").resolve(),
+                (workspace / "two.py").resolve(),
+            ]:
+                f.write_text('print("hello")\n')
+            self.invokeBlack([str(workspace)])
+
+    @event_loop()

     def test_check_diff_use_together(self) -> None:
         with cache_dir():
             # Files which will be reformatted.
     def test_check_diff_use_together(self) -> None:
         with cache_dir():
             # Files which will be reformatted.


@@ -1147,20 +1218,19 @@ class BlackTestCase(unittest.TestCase):
             self.invokeBlack([str(workspace.resolve())])
 
     def test_read_cache_line_lengths(self) -> None:
             self.invokeBlack([str(workspace.resolve())])
 
     def test_read_cache_line_lengths(self) -> None:

-        mode = black.FileMode()
-        short_mode = black.FileMode(line_length=1)
+        mode = DEFAULT_MODE
+        short_mode = replace(DEFAULT_MODE, line_length=1)

         with cache_dir() as workspace:
             path = (workspace / "file.py").resolve()
             path.touch()
             black.write_cache({}, [path], mode)
             one = black.read_cache(mode)
         with cache_dir() as workspace:
             path = (workspace / "file.py").resolve()
             path.touch()
             black.write_cache({}, [path], mode)
             one = black.read_cache(mode)

-            self.assertIn(path, one)
+            self.assertIn(str(path), one)

             two = black.read_cache(short_mode)
             two = black.read_cache(short_mode)

-            self.assertNotIn(path, two)
+            self.assertNotIn(str(path), two)

 
     def test_single_file_force_pyi(self) -> None:
 
     def test_single_file_force_pyi(self) -> None:

-        reg_mode = black.FileMode()
-        pyi_mode = black.FileMode(is_pyi=True)
+        pyi_mode = replace(DEFAULT_MODE, is_pyi=True)

         contents, expected = read_data("force_pyi")
         with cache_dir() as workspace:
             path = (workspace / "file.py").resolve()
         contents, expected = read_data("force_pyi")
         with cache_dir() as workspace:
             path = (workspace / "file.py").resolve()


@@ -1171,15 +1241,17 @@ class BlackTestCase(unittest.TestCase):
                 actual = fh.read()
             # verify cache with --pyi is separate
             pyi_cache = black.read_cache(pyi_mode)
                 actual = fh.read()
             # verify cache with --pyi is separate
             pyi_cache = black.read_cache(pyi_mode)

-            self.assertIn(path, pyi_cache)
-            normal_cache = black.read_cache(reg_mode)
-            self.assertNotIn(path, normal_cache)
-        self.assertEqual(actual, expected)
+            self.assertIn(str(path), pyi_cache)
+            normal_cache = black.read_cache(DEFAULT_MODE)
+            self.assertNotIn(str(path), normal_cache)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(contents, actual)
+        black.assert_stable(contents, actual, pyi_mode)

 
 

-    @event_loop(close=False)
+    @event_loop()

     def test_multi_file_force_pyi(self) -> None:
     def test_multi_file_force_pyi(self) -> None:

-        reg_mode = black.FileMode()
-        pyi_mode = black.FileMode(is_pyi=True)
+        reg_mode = DEFAULT_MODE
+        pyi_mode = replace(DEFAULT_MODE, is_pyi=True)

         contents, expected = read_data("force_pyi")
         with cache_dir() as workspace:
             paths = [
         contents, expected = read_data("force_pyi")
         with cache_dir() as workspace:
             paths = [


@@ -1198,8 +1270,8 @@ class BlackTestCase(unittest.TestCase):
             pyi_cache = black.read_cache(pyi_mode)
             normal_cache = black.read_cache(reg_mode)
             for path in paths:
             pyi_cache = black.read_cache(pyi_mode)
             normal_cache = black.read_cache(reg_mode)
             for path in paths:

-                self.assertIn(path, pyi_cache)
-                self.assertNotIn(path, normal_cache)
+                self.assertIn(str(path), pyi_cache)
+                self.assertNotIn(str(path), normal_cache)

 
     def test_pipe_force_pyi(self) -> None:
         source, expected = read_data("force_pyi")
 
     def test_pipe_force_pyi(self) -> None:
         source, expected = read_data("force_pyi")


@@ -1211,8 +1283,8 @@ class BlackTestCase(unittest.TestCase):
         self.assertFormatEqual(actual, expected)
 
     def test_single_file_force_py36(self) -> None:
         self.assertFormatEqual(actual, expected)
 
     def test_single_file_force_py36(self) -> None:

-        reg_mode = black.FileMode()
-        py36_mode = black.FileMode(target_versions=black.PY36_VERSIONS)
+        reg_mode = DEFAULT_MODE
+        py36_mode = replace(DEFAULT_MODE, target_versions=PY36_VERSIONS)

         source, expected = read_data("force_py36")
         with cache_dir() as workspace:
             path = (workspace / "file.py").resolve()
         source, expected = read_data("force_py36")
         with cache_dir() as workspace:
             path = (workspace / "file.py").resolve()


@@ -1223,15 +1295,15 @@ class BlackTestCase(unittest.TestCase):
                 actual = fh.read()
             # verify cache with --target-version is separate
             py36_cache = black.read_cache(py36_mode)
                 actual = fh.read()
             # verify cache with --target-version is separate
             py36_cache = black.read_cache(py36_mode)

-            self.assertIn(path, py36_cache)
+            self.assertIn(str(path), py36_cache)

             normal_cache = black.read_cache(reg_mode)
             normal_cache = black.read_cache(reg_mode)

-            self.assertNotIn(path, normal_cache)
+            self.assertNotIn(str(path), normal_cache)

         self.assertEqual(actual, expected)
 
         self.assertEqual(actual, expected)
 

-    @event_loop(close=False)
+    @event_loop()

     def test_multi_file_force_py36(self) -> None:
     def test_multi_file_force_py36(self) -> None:

-        reg_mode = black.FileMode()
-        py36_mode = black.FileMode(target_versions=black.PY36_VERSIONS)
+        reg_mode = DEFAULT_MODE
+        py36_mode = replace(DEFAULT_MODE, target_versions=PY36_VERSIONS)

         source, expected = read_data("force_py36")
         with cache_dir() as workspace:
             paths = [
         source, expected = read_data("force_py36")
         with cache_dir() as workspace:
             paths = [


@@ -1250,8 +1322,8 @@ class BlackTestCase(unittest.TestCase):
             pyi_cache = black.read_cache(py36_mode)
             normal_cache = black.read_cache(reg_mode)
             for path in paths:
             pyi_cache = black.read_cache(py36_mode)
             normal_cache = black.read_cache(reg_mode)
             for path in paths:

-                self.assertIn(path, pyi_cache)
-                self.assertNotIn(path, normal_cache)
+                self.assertIn(str(path), pyi_cache)
+                self.assertNotIn(str(path), normal_cache)

 
     def test_pipe_force_py36(self) -> None:
         source, expected = read_data("force_py36")
 
     def test_pipe_force_py36(self) -> None:
         source, expected = read_data("force_py36")


@@ -1269,6 +1341,7 @@ class BlackTestCase(unittest.TestCase):
         include = re.compile(r"\.pyi?$")
         exclude = re.compile(r"/exclude/|/\.definitely_exclude/")
         report = black.Report()
         include = re.compile(r"\.pyi?$")
         exclude = re.compile(r"/exclude/|/\.definitely_exclude/")
         report = black.Report()

+        gitignore = PathSpec.from_lines("gitwildmatch", [])

         sources: List[Path] = []
         expected = [
             Path(path / "b/dont_exclude/a.py"),
         sources: List[Path] = []
         expected = [
             Path(path / "b/dont_exclude/a.py"),


@@ -1276,13 +1349,268 @@ class BlackTestCase(unittest.TestCase):
         ]
         this_abs = THIS_DIR.resolve()
         sources.extend(
         ]
         this_abs = THIS_DIR.resolve()
         sources.extend(

-            black.gen_python_files_in_dir(path, this_abs, include, exclude, report)
+            black.gen_python_files(
+                path.iterdir(),
+                this_abs,
+                include,
+                exclude,
+                None,
+                None,
+                report,
+                gitignore,
+            )
+        )
+        self.assertEqual(sorted(expected), sorted(sources))
+
+    @patch("black.find_project_root", lambda *args: THIS_DIR.resolve())
+    def test_exclude_for_issue_1572(self) -> None:
+        # Exclude shouldn't touch files that were explicitly given to Black through the
+        # CLI. Exclude is supposed to only apply to the recursive discovery of files.
+        # https://github.com/psf/black/issues/1572
+        path = THIS_DIR / "data" / "include_exclude_tests"
+        include = ""
+        exclude = r"/exclude/|a\.py"
+        src = str(path / "b/exclude/a.py")
+        report = black.Report()
+        expected = [Path(path / "b/exclude/a.py")]
+        sources = list(
+            black.get_sources(
+                ctx=FakeContext(),
+                src=(src,),
+                quiet=True,
+                verbose=False,
+                include=re.compile(include),
+                exclude=re.compile(exclude),
+                extend_exclude=None,
+                force_exclude=None,
+                report=report,
+                stdin_filename=None,
+            )
+        )
+        self.assertEqual(sorted(expected), sorted(sources))
+
+    @patch("black.find_project_root", lambda *args: THIS_DIR.resolve())
+    def test_get_sources_with_stdin(self) -> None:
+        include = ""
+        exclude = r"/exclude/|a\.py"
+        src = "-"
+        report = black.Report()
+        expected = [Path("-")]
+        sources = list(
+            black.get_sources(
+                ctx=FakeContext(),
+                src=(src,),
+                quiet=True,
+                verbose=False,
+                include=re.compile(include),
+                exclude=re.compile(exclude),
+                extend_exclude=None,
+                force_exclude=None,
+                report=report,
+                stdin_filename=None,
+            )
+        )
+        self.assertEqual(sorted(expected), sorted(sources))
+
+    @patch("black.find_project_root", lambda *args: THIS_DIR.resolve())
+    def test_get_sources_with_stdin_filename(self) -> None:
+        include = ""
+        exclude = r"/exclude/|a\.py"
+        src = "-"
+        report = black.Report()
+        stdin_filename = str(THIS_DIR / "data/collections.py")
+        expected = [Path(f"__BLACK_STDIN_FILENAME__{stdin_filename}")]
+        sources = list(
+            black.get_sources(
+                ctx=FakeContext(),
+                src=(src,),
+                quiet=True,
+                verbose=False,
+                include=re.compile(include),
+                exclude=re.compile(exclude),
+                extend_exclude=None,
+                force_exclude=None,
+                report=report,
+                stdin_filename=stdin_filename,
+            )
+        )
+        self.assertEqual(sorted(expected), sorted(sources))
+
+    @patch("black.find_project_root", lambda *args: THIS_DIR.resolve())
+    def test_get_sources_with_stdin_filename_and_exclude(self) -> None:
+        # Exclude shouldn't exclude stdin_filename since it is mimicing the
+        # file being passed directly. This is the same as
+        # test_exclude_for_issue_1572
+        path = THIS_DIR / "data" / "include_exclude_tests"
+        include = ""
+        exclude = r"/exclude/|a\.py"
+        src = "-"
+        report = black.Report()
+        stdin_filename = str(path / "b/exclude/a.py")
+        expected = [Path(f"__BLACK_STDIN_FILENAME__{stdin_filename}")]
+        sources = list(
+            black.get_sources(
+                ctx=FakeContext(),
+                src=(src,),
+                quiet=True,
+                verbose=False,
+                include=re.compile(include),
+                exclude=re.compile(exclude),
+                extend_exclude=None,
+                force_exclude=None,
+                report=report,
+                stdin_filename=stdin_filename,
+            )
+        )
+        self.assertEqual(sorted(expected), sorted(sources))
+
+    @patch("black.find_project_root", lambda *args: THIS_DIR.resolve())
+    def test_get_sources_with_stdin_filename_and_extend_exclude(self) -> None:
+        # Extend exclude shouldn't exclude stdin_filename since it is mimicking the
+        # file being passed directly. This is the same as
+        # test_exclude_for_issue_1572
+        path = THIS_DIR / "data" / "include_exclude_tests"
+        include = ""
+        extend_exclude = r"/exclude/|a\.py"
+        src = "-"
+        report = black.Report()
+        stdin_filename = str(path / "b/exclude/a.py")
+        expected = [Path(f"__BLACK_STDIN_FILENAME__{stdin_filename}")]
+        sources = list(
+            black.get_sources(
+                ctx=FakeContext(),
+                src=(src,),
+                quiet=True,
+                verbose=False,
+                include=re.compile(include),
+                exclude=re.compile(""),
+                extend_exclude=re.compile(extend_exclude),
+                force_exclude=None,
+                report=report,
+                stdin_filename=stdin_filename,
+            )
+        )
+        self.assertEqual(sorted(expected), sorted(sources))
+
+    @patch("black.find_project_root", lambda *args: THIS_DIR.resolve())
+    def test_get_sources_with_stdin_filename_and_force_exclude(self) -> None:
+        # Force exclude should exclude the file when passing it through
+        # stdin_filename
+        path = THIS_DIR / "data" / "include_exclude_tests"
+        include = ""
+        force_exclude = r"/exclude/|a\.py"
+        src = "-"
+        report = black.Report()
+        stdin_filename = str(path / "b/exclude/a.py")
+        sources = list(
+            black.get_sources(
+                ctx=FakeContext(),
+                src=(src,),
+                quiet=True,
+                verbose=False,
+                include=re.compile(include),
+                exclude=re.compile(""),
+                extend_exclude=None,
+                force_exclude=re.compile(force_exclude),
+                report=report,
+                stdin_filename=stdin_filename,
+            )
+        )
+        self.assertEqual([], sorted(sources))
+
+    def test_reformat_one_with_stdin(self) -> None:
+        with patch(
+            "black.format_stdin_to_stdout",
+            return_value=lambda *args, **kwargs: black.Changed.YES,
+        ) as fsts:
+            report = MagicMock()
+            path = Path("-")
+            black.reformat_one(
+                path,
+                fast=True,
+                write_back=black.WriteBack.YES,
+                mode=DEFAULT_MODE,
+                report=report,
+            )
+            fsts.assert_called_once()
+            report.done.assert_called_with(path, black.Changed.YES)
+
+    def test_reformat_one_with_stdin_filename(self) -> None:
+        with patch(
+            "black.format_stdin_to_stdout",
+            return_value=lambda *args, **kwargs: black.Changed.YES,
+        ) as fsts:
+            report = MagicMock()
+            p = "foo.py"
+            path = Path(f"__BLACK_STDIN_FILENAME__{p}")
+            expected = Path(p)
+            black.reformat_one(
+                path,
+                fast=True,
+                write_back=black.WriteBack.YES,
+                mode=DEFAULT_MODE,
+                report=report,
+            )
+            fsts.assert_called_once()
+            # __BLACK_STDIN_FILENAME__ should have been striped
+            report.done.assert_called_with(expected, black.Changed.YES)
+
+    def test_reformat_one_with_stdin_and_existing_path(self) -> None:
+        with patch(
+            "black.format_stdin_to_stdout",
+            return_value=lambda *args, **kwargs: black.Changed.YES,
+        ) as fsts:
+            report = MagicMock()
+            # Even with an existing file, since we are forcing stdin, black
+            # should output to stdout and not modify the file inplace
+            p = Path(str(THIS_DIR / "data/collections.py"))
+            # Make sure is_file actually returns True
+            self.assertTrue(p.is_file())
+            path = Path(f"__BLACK_STDIN_FILENAME__{p}")
+            expected = Path(p)
+            black.reformat_one(
+                path,
+                fast=True,
+                write_back=black.WriteBack.YES,
+                mode=DEFAULT_MODE,
+                report=report,
+            )
+            fsts.assert_called_once()
+            # __BLACK_STDIN_FILENAME__ should have been striped
+            report.done.assert_called_with(expected, black.Changed.YES)
+
+    def test_gitignore_exclude(self) -> None:
+        path = THIS_DIR / "data" / "include_exclude_tests"
+        include = re.compile(r"\.pyi?$")
+        exclude = re.compile(r"")
+        report = black.Report()
+        gitignore = PathSpec.from_lines(
+            "gitwildmatch", ["exclude/", ".definitely_exclude"]
+        )
+        sources: List[Path] = []
+        expected = [
+            Path(path / "b/dont_exclude/a.py"),
+            Path(path / "b/dont_exclude/a.pyi"),
+        ]
+        this_abs = THIS_DIR.resolve()
+        sources.extend(
+            black.gen_python_files(
+                path.iterdir(),
+                this_abs,
+                include,
+                exclude,
+                None,
+                None,
+                report,
+                gitignore,
+            )

         )
         self.assertEqual(sorted(expected), sorted(sources))
 
     def test_empty_include(self) -> None:
         path = THIS_DIR / "data" / "include_exclude_tests"
         report = black.Report()
         )
         self.assertEqual(sorted(expected), sorted(sources))
 
     def test_empty_include(self) -> None:
         path = THIS_DIR / "data" / "include_exclude_tests"
         report = black.Report()

+        gitignore = PathSpec.from_lines("gitwildmatch", [])

         empty = re.compile(r"")
         sources: List[Path] = []
         expected = [
         empty = re.compile(r"")
         sources: List[Path] = []
         expected = [


@@ -1298,35 +1626,45 @@ class BlackTestCase(unittest.TestCase):
         ]
         this_abs = THIS_DIR.resolve()
         sources.extend(
         ]
         this_abs = THIS_DIR.resolve()
         sources.extend(

-            black.gen_python_files_in_dir(
-                path, this_abs, empty, re.compile(black.DEFAULT_EXCLUDES), report
+            black.gen_python_files(
+                path.iterdir(),
+                this_abs,
+                empty,
+                re.compile(black.DEFAULT_EXCLUDES),
+                None,
+                None,
+                report,
+                gitignore,

             )
         )
         self.assertEqual(sorted(expected), sorted(sources))
 
             )
         )
         self.assertEqual(sorted(expected), sorted(sources))
 

-    def test_empty_exclude(self) -> None:
+    def test_extend_exclude(self) -> None:

         path = THIS_DIR / "data" / "include_exclude_tests"
         report = black.Report()
         path = THIS_DIR / "data" / "include_exclude_tests"
         report = black.Report()

-        empty = re.compile(r"")
+        gitignore = PathSpec.from_lines("gitwildmatch", [])

         sources: List[Path] = []
         expected = [
         sources: List[Path] = []
         expected = [

-            Path(path / "b/dont_exclude/a.py"),
-            Path(path / "b/dont_exclude/a.pyi"),

             Path(path / "b/exclude/a.py"),
             Path(path / "b/exclude/a.py"),

-            Path(path / "b/exclude/a.pyi"),
-            Path(path / "b/.definitely_exclude/a.py"),
-            Path(path / "b/.definitely_exclude/a.pyi"),
+            Path(path / "b/dont_exclude/a.py"),

         ]
         this_abs = THIS_DIR.resolve()
         sources.extend(
         ]
         this_abs = THIS_DIR.resolve()
         sources.extend(

-            black.gen_python_files_in_dir(
-                path, this_abs, re.compile(black.DEFAULT_INCLUDES), empty, report
+            black.gen_python_files(
+                path.iterdir(),
+                this_abs,
+                re.compile(black.DEFAULT_INCLUDES),
+                re.compile(r"\.pyi$"),
+                re.compile(r"\.definitely_exclude"),
+                None,
+                report,
+                gitignore,

             )
         )
         self.assertEqual(sorted(expected), sorted(sources))
 
             )
         )
         self.assertEqual(sorted(expected), sorted(sources))
 

-    def test_invalid_include_exclude(self) -> None:
-        for option in ["--include", "--exclude"]:
+    def test_invalid_cli_regex(self) -> None:
+        for option in ["--include", "--exclude", "--extend-exclude", "--force-exclude"]:

             self.invokeBlack(["-", option, "**()(!!*)"], exit_code=2)
 
     def test_preserves_line_endings(self) -> None:
             self.invokeBlack(["-", option, "**()(!!*)"], exit_code=2)
 
     def test_preserves_line_endings(self) -> None:


@@ -1360,18 +1698,31 @@ class BlackTestCase(unittest.TestCase):
 
     def test_symlink_out_of_root_directory(self) -> None:
         path = MagicMock()
 
     def test_symlink_out_of_root_directory(self) -> None:
         path = MagicMock()

-        root = THIS_DIR
+        root = THIS_DIR.resolve()

         child = MagicMock()
         include = re.compile(black.DEFAULT_INCLUDES)
         exclude = re.compile(black.DEFAULT_EXCLUDES)
         report = black.Report()
         child = MagicMock()
         include = re.compile(black.DEFAULT_INCLUDES)
         exclude = re.compile(black.DEFAULT_EXCLUDES)
         report = black.Report()

+        gitignore = PathSpec.from_lines("gitwildmatch", [])

         # `child` should behave like a symlink which resolved path is clearly
         # outside of the `root` directory.
         path.iterdir.return_value = [child]
         child.resolve.return_value = Path("/a/b/c")
         # `child` should behave like a symlink which resolved path is clearly
         # outside of the `root` directory.
         path.iterdir.return_value = [child]
         child.resolve.return_value = Path("/a/b/c")

+        child.as_posix.return_value = "/a/b/c"

         child.is_symlink.return_value = True
         try:
         child.is_symlink.return_value = True
         try:

-            list(black.gen_python_files_in_dir(path, root, include, exclude, report))
+            list(
+                black.gen_python_files(
+                    path.iterdir(),
+                    root,
+                    include,
+                    exclude,
+                    None,
+                    None,
+                    report,
+                    gitignore,
+                )
+            )

         except ValueError as ve:
             self.fail(f"`get_python_files_in_dir()` failed: {ve}")
         path.iterdir.assert_called_once()
         except ValueError as ve:
             self.fail(f"`get_python_files_in_dir()` failed: {ve}")
         path.iterdir.assert_called_once()


@@ -1381,7 +1732,18 @@ class BlackTestCase(unittest.TestCase):
         # outside of the `root` directory.
         child.is_symlink.return_value = False
         with self.assertRaises(ValueError):
         # outside of the `root` directory.
         child.is_symlink.return_value = False
         with self.assertRaises(ValueError):

-            list(black.gen_python_files_in_dir(path, root, include, exclude, report))
+            list(
+                black.gen_python_files(
+                    path.iterdir(),
+                    root,
+                    include,
+                    exclude,
+                    None,
+                    None,
+                    report,
+                    gitignore,
+                )
+            )

         path.iterdir.assert_called()
         self.assertEqual(path.iterdir.call_count, 2)
         child.resolve.assert_called()
         path.iterdir.assert_called()
         self.assertEqual(path.iterdir.call_count, 2)
         child.resolve.assert_called()


@@ -1426,169 +1788,161 @@ class BlackTestCase(unittest.TestCase):
         ):
             ff(THIS_FILE)
 
         ):
             ff(THIS_FILE)
 

-    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
-    @async_test
-    async def test_blackd_request_needs_formatting(self) -> None:
-        app = blackd.make_app()
-        async with TestClient(TestServer(app)) as client:
-            response = await client.post("/", data=b"print('hello world')")
-            self.assertEqual(response.status, 200)
-            self.assertEqual(response.charset, "utf8")
-            self.assertEqual(await response.read(), b'print("hello world")\n')
-
-    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
-    @async_test
-    async def test_blackd_request_no_change(self) -> None:
-        app = blackd.make_app()
-        async with TestClient(TestServer(app)) as client:
-            response = await client.post("/", data=b'print("hello world")\n')
-            self.assertEqual(response.status, 204)
-            self.assertEqual(await response.read(), b"")
-
-    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
-    @async_test
-    async def test_blackd_request_syntax_error(self) -> None:
-        app = blackd.make_app()
-        async with TestClient(TestServer(app)) as client:
-            response = await client.post("/", data=b"what even ( is")
-            self.assertEqual(response.status, 400)
-            content = await response.text()
-            self.assertTrue(
-                content.startswith("Cannot parse"),
-                msg=f"Expected error to start with 'Cannot parse', got {repr(content)}",
-            )
+    def test_invalid_config_return_code(self) -> None:
+        tmp_file = Path(black.dump_to_file())
+        try:
+            tmp_config = Path(black.dump_to_file())
+            tmp_config.unlink()
+            args = ["--config", str(tmp_config), str(tmp_file)]
+            self.invokeBlack(args, exit_code=2, ignore_config=False)
+        finally:
+            tmp_file.unlink()
+
+    def test_parse_pyproject_toml(self) -> None:
+        test_toml_file = THIS_DIR / "test.toml"
+        config = black.parse_pyproject_toml(str(test_toml_file))
+        self.assertEqual(config["verbose"], 1)
+        self.assertEqual(config["check"], "no")
+        self.assertEqual(config["diff"], "y")
+        self.assertEqual(config["color"], True)
+        self.assertEqual(config["line_length"], 79)
+        self.assertEqual(config["target_version"], ["py36", "py37", "py38"])
+        self.assertEqual(config["exclude"], r"\.pyi?$")
+        self.assertEqual(config["include"], r"\.py?$")
+
+    def test_read_pyproject_toml(self) -> None:
+        test_toml_file = THIS_DIR / "test.toml"
+        fake_ctx = FakeContext()
+        black.read_pyproject_toml(fake_ctx, FakeParameter(), str(test_toml_file))
+        config = fake_ctx.default_map
+        self.assertEqual(config["verbose"], "1")
+        self.assertEqual(config["check"], "no")
+        self.assertEqual(config["diff"], "y")
+        self.assertEqual(config["color"], "True")
+        self.assertEqual(config["line_length"], "79")
+        self.assertEqual(config["target_version"], ["py36", "py37", "py38"])
+        self.assertEqual(config["exclude"], r"\.pyi?$")
+        self.assertEqual(config["include"], r"\.py?$")
+
+    def test_find_project_root(self) -> None:
+        with TemporaryDirectory() as workspace:
+            root = Path(workspace)
+            test_dir = root / "test"
+            test_dir.mkdir()

 
 

-    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
-    @async_test
-    async def test_blackd_unsupported_version(self) -> None:
-        app = blackd.make_app()
-        async with TestClient(TestServer(app)) as client:
-            response = await client.post(
-                "/", data=b"what", headers={blackd.VERSION_HEADER: "2"}
-            )
-            self.assertEqual(response.status, 501)
-
-    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
-    @async_test
-    async def test_blackd_supported_version(self) -> None:
-        app = blackd.make_app()
-        async with TestClient(TestServer(app)) as client:
-            response = await client.post(
-                "/", data=b"what", headers={blackd.VERSION_HEADER: "1"}
-            )
-            self.assertEqual(response.status, 200)
-
-    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
-    @async_test
-    async def test_blackd_invalid_python_variant(self) -> None:
-        app = blackd.make_app()
-        async with TestClient(TestServer(app)) as client:
-
-            async def check(header_value: str, expected_status: int = 400) -> None:
-                response = await client.post(
-                    "/",
-                    data=b"what",
-                    headers={blackd.PYTHON_VARIANT_HEADER: header_value},
-                )
-                self.assertEqual(response.status, expected_status)
-
-            await check("lol")
-            await check("ruby3.5")
-            await check("pyi3.6")
-            await check("py1.5")
-            await check("2.8")
-            await check("py2.8")
-            await check("3.0")
-            await check("pypy3.0")
-            await check("jython3.4")
-
-    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
-    @async_test
-    async def test_blackd_pyi(self) -> None:
-        app = blackd.make_app()
-        async with TestClient(TestServer(app)) as client:
-            source, expected = read_data("stub.pyi")
-            response = await client.post(
-                "/", data=source, headers={blackd.PYTHON_VARIANT_HEADER: "pyi"}
+            src_dir = root / "src"
+            src_dir.mkdir()
+
+            root_pyproject = root / "pyproject.toml"
+            root_pyproject.touch()
+            src_pyproject = src_dir / "pyproject.toml"
+            src_pyproject.touch()
+            src_python = src_dir / "foo.py"
+            src_python.touch()
+
+            self.assertEqual(
+                black.find_project_root((src_dir, test_dir)), root.resolve()

             )
             )

-            self.assertEqual(response.status, 200)
-            self.assertEqual(await response.text(), expected)
-
-    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
-    @async_test
-    async def test_blackd_python_variant(self) -> None:
-        app = blackd.make_app()
-        code = (
-            "def f(\n"
-            "    and_has_a_bunch_of,\n"
-            "    very_long_arguments_too,\n"
-            "    and_lots_of_them_as_well_lol,\n"
-            "    **and_very_long_keyword_arguments\n"
-            "):\n"
-            "    pass\n"
-        )
-        async with TestClient(TestServer(app)) as client:
+            self.assertEqual(black.find_project_root((src_dir,)), src_dir.resolve())
+            self.assertEqual(black.find_project_root((src_python,)), src_dir.resolve())

 
 

-            async def check(header_value: str, expected_status: int) -> None:
-                response = await client.post(
-                    "/", data=code, headers={blackd.PYTHON_VARIANT_HEADER: header_value}
-                )
-                self.assertEqual(response.status, expected_status)
-
-            await check("3.6", 200)
-            await check("py3.6", 200)
-            await check("3.6,3.7", 200)
-            await check("3.6,py3.7", 200)
-
-            await check("2", 204)
-            await check("2.7", 204)
-            await check("py2.7", 204)
-            await check("3.4", 204)
-            await check("py3.4", 204)
-
-    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
-    @async_test
-    async def test_blackd_fast(self) -> None:
-        with open(os.devnull, "w") as dn, redirect_stderr(dn):
-            app = blackd.make_app()
-            async with TestClient(TestServer(app)) as client:
-                response = await client.post("/", data=b"ur'hello'")
-                self.assertEqual(response.status, 500)
-                self.assertIn("failed to parse source file", await response.text())
-                response = await client.post(
-                    "/", data=b"ur'hello'", headers={blackd.FAST_OR_SAFE_HEADER: "fast"}
+    @patch("black.find_user_pyproject_toml", black.find_user_pyproject_toml.__wrapped__)
+    def test_find_user_pyproject_toml_linux(self) -> None:
+        if system() == "Windows":
+            return
+
+        # Test if XDG_CONFIG_HOME is checked
+        with TemporaryDirectory() as workspace:
+            tmp_user_config = Path(workspace) / "black"
+            with patch.dict("os.environ", {"XDG_CONFIG_HOME": workspace}):
+                self.assertEqual(
+                    black.find_user_pyproject_toml(), tmp_user_config.resolve()

                 )
                 )

-                self.assertEqual(response.status, 200)
-
-    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
-    @async_test
-    async def test_blackd_line_length(self) -> None:
-        app = blackd.make_app()
-        async with TestClient(TestServer(app)) as client:
-            response = await client.post(
-                "/", data=b'print("hello")\n', headers={blackd.LINE_LENGTH_HEADER: "7"}
-            )
-            self.assertEqual(response.status, 200)
-
-    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
-    @async_test
-    async def test_blackd_invalid_line_length(self) -> None:
-        app = blackd.make_app()
-        async with TestClient(TestServer(app)) as client:
-            response = await client.post(
-                "/",
-                data=b'print("hello")\n',
-                headers={blackd.LINE_LENGTH_HEADER: "NaN"},
+
+        # Test fallback for XDG_CONFIG_HOME
+        with patch.dict("os.environ"):
+            os.environ.pop("XDG_CONFIG_HOME", None)
+            fallback_user_config = Path("~/.config").expanduser() / "black"
+            self.assertEqual(
+                black.find_user_pyproject_toml(), fallback_user_config.resolve()

             )
             )

-            self.assertEqual(response.status, 400)
-
-    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
-    def test_blackd_main(self) -> None:
-        with patch("blackd.web.run_app"):
-            result = CliRunner().invoke(blackd.main, [])
-            if result.exception is not None:
-                raise result.exception
+
+    def test_find_user_pyproject_toml_windows(self) -> None:
+        if system() != "Windows":
+            return
+
+        user_config_path = Path.home() / ".black"
+        self.assertEqual(black.find_user_pyproject_toml(), user_config_path.resolve())
+
+    def test_bpo_33660_workaround(self) -> None:
+        if system() == "Windows":
+            return
+
+        # https://bugs.python.org/issue33660
+
+        old_cwd = Path.cwd()
+        try:
+            root = Path("/")
+            os.chdir(str(root))
+            path = Path("workspace") / "project"
+            report = black.Report(verbose=True)
+            normalized_path = black.normalize_path_maybe_ignore(path, root, report)
+            self.assertEqual(normalized_path, "workspace/project")
+        finally:
+            os.chdir(str(old_cwd))
+
+    def test_newline_comment_interaction(self) -> None:
+        source = "class A:\\\r\n# type: ignore\n pass\n"
+        output = black.format_str(source, mode=DEFAULT_MODE)
+        black.assert_stable(source, output, mode=DEFAULT_MODE)
+
+    def test_bpo_2142_workaround(self) -> None:
+
+        # https://bugs.python.org/issue2142
+
+        source, _ = read_data("missing_final_newline.py")
+        # read_data adds a trailing newline
+        source = source.rstrip()
+        expected, _ = read_data("missing_final_newline.diff")
+        tmp_file = Path(black.dump_to_file(source, ensure_final_newline=False))
+        diff_header = re.compile(
+            rf"{re.escape(str(tmp_file))}\t\d\d\d\d-\d\d-\d\d "
+            r"\d\d:\d\d:\d\d\.\d\d\d\d\d\d \+\d\d\d\d"
+        )
+        try:
+            result = BlackRunner().invoke(black.main, ["--diff", str(tmp_file)])

             self.assertEqual(result.exit_code, 0)
             self.assertEqual(result.exit_code, 0)

+        finally:
+            os.unlink(tmp_file)
+        actual = result.output
+        actual = diff_header.sub(DETERMINISTIC_HEADER, actual)
+        self.assertEqual(actual, expected)
+
+
+with open(black.__file__, "r", encoding="utf-8") as _bf:
+    black_source_lines = _bf.readlines()
+
+
+def tracefunc(frame: types.FrameType, event: str, arg: Any) -> Callable:
+    """Show function calls `from black/__init__.py` as they happen.
+
+    Register this with `sys.settrace()` in a test you're debugging.
+    """
+    if event != "call":
+        return tracefunc
+
+    stack = len(inspect.stack()) - 19
+    stack *= 2
+    filename = frame.f_code.co_filename
+    lineno = frame.f_lineno
+    func_sig_lineno = lineno - 1
+    funcname = black_source_lines[func_sig_lineno].strip()
+    while funcname.startswith("@"):
+        func_sig_lineno += 1
+        funcname = black_source_lines[func_sig_lineno].strip()
+    if "black/__init__.py" in filename:
+        print(f"{' ' * stack}{lineno}:{funcname}")
+    return tracefunc

 
 
 if __name__ == "__main__":
 
 
 if __name__ == "__main__":