Use optional tests for "no_python2" to simplify local testing (#2203)

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

diff --git a/tests/test_black.py b/tests/test_black.py
index b4820531fab62d860808b37448881ccf3b494a78..b8e526a953eccb7c719b9b29dab81d9bfe5fb5e3 100644 (file)
--- a/tests/test_black.py
+++ b/tests/test_black.py
@@ -1,53 +1,66 @@
 #!/usr/bin/env python3
 #!/usr/bin/env python3

+import multiprocessing

 import asyncio
 import asyncio

+import logging
+from concurrent.futures import ThreadPoolExecutor

 from contextlib import contextmanager
 from contextlib import contextmanager

-from functools import partial
-from io import StringIO
+from dataclasses import replace
+import inspect
+from io import BytesIO, TextIOWrapper

 import os
 from pathlib import Path
 import os
 from pathlib import Path

+from platform import system
+import regex as re

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

-from typing import Any, List, Tuple, Iterator
+import types
+from typing import (
+    Any,
+    BinaryIO,
+    Callable,
+    Dict,
+    Generator,
+    List,
+    Iterator,
+    TypeVar,
+)
+import pytest

 import unittest
 import unittest

-from unittest.mock import patch
+from unittest.mock import patch, MagicMock

 
 

+import click

 from click import unstyle
 from click.testing import CliRunner
 
 import black
 from click import unstyle
 from click.testing import CliRunner
 
 import black

+from black import Feature, TargetVersion

 
 

-ll = 88
-ff = partial(black.format_file_in_place, line_length=ll, fast=True)
-fs = partial(black.format_str, line_length=ll)
-THIS_FILE = Path(__file__)
-THIS_DIR = THIS_FILE.parent
-EMPTY_LINE = "# EMPTY LINE WITH WHITESPACE" + " (this comment will be removed)"
-
+from pathspec import PathSpec

 
 

-def dump_to_stderr(*output: str) -> str:
-    return "\n" + "\n".join(output) + "\n"
+# 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

 
 
 
 

-def read_data(name: str) -> Tuple[str, str]:
-    """read_data('test_name') -> 'input', 'output'"""
-    if not name.endswith((".py", ".out", ".diff")):
-        name += ".py"
-    _input: List[str] = []
-    _output: List[str] = []
-    with open(THIS_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"
+THIS_FILE = Path(__file__)
+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")

 
 
 @contextmanager
 
 
 @contextmanager


@@ -56,124 +69,243 @@ def cache_dir(exists: bool = True) -> Iterator[Path]:
         cache_dir = Path(workspace)
         if not exists:
             cache_dir = cache_dir / "new"
         cache_dir = Path(workspace)
         if not exists:
             cache_dir = cache_dir / "new"

-        cache_file = cache_dir / "cache.pkl"
-        with patch("black.CACHE_DIR", cache_dir), patch("black.CACHE_FILE", cache_file):
+        with patch("black.CACHE_DIR", cache_dir):

             yield cache_dir
 
 
 @contextmanager
             yield cache_dir
 
 
 @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 BlackTestCase(unittest.TestCase):
-    maxDiff = None
+class FakeContext(click.Context):
+    """A fake click Context for when calling functions that need it."""

 
 

-    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)
+    def __init__(self) -> None:
+        self.default_map: Dict[str, Any] = {}

 
 

-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_self(self) -> None:
-        source, expected = read_data("test_black")
-        actual = fs(source)
-        self.assertFormatEqual(expected, actual)
-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, line_length=ll)
-        self.assertFalse(ff(THIS_FILE))
+
+class FakeParameter(click.Parameter):
+    """A fake click Parameter for when calling functions that need it."""
+
+    def __init__(self) -> None:
+        pass
+
+
+class BlackRunner(CliRunner):
+    """Modify CliRunner so that stderr is not merged with stdout.
+
+    This is a hack that can be removed once we depend on Click 7.x"""
+
+    def __init__(self) -> None:
+        self.stderrbuf = BytesIO()
+        self.stdoutbuf = BytesIO()
+        self.stdout_bytes = b""
+        self.stderr_bytes = b""
+        super().__init__()
+
+    @contextmanager
+    def isolation(self, *args: Any, **kwargs: Any) -> Generator[BinaryIO, None, None]:
+        with super().isolation(*args, **kwargs) as output:
+            try:
+                hold_stderr = sys.stderr
+                sys.stderr = TextIOWrapper(self.stderrbuf, encoding=self.charset)
+                yield output
+            finally:
+                self.stdout_bytes = sys.stdout.buffer.getvalue()  # type: ignore
+                self.stderr_bytes = sys.stderr.buffer.getvalue()  # type: ignore
+                sys.stderr = hold_stderr
+
+
+class BlackTestCase(BlackBaseTestCase):
+    def invokeBlack(
+        self, args: List[str], exit_code: int = 0, ignore_config: bool = True
+    ) -> None:
+        runner = BlackRunner()
+        if ignore_config:
+            args = ["--verbose", "--config", str(THIS_DIR / "empty.toml"), *args]
+        result = runner.invoke(black.main, args)
+        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)
 
     @patch("black.dump_to_file", dump_to_stderr)

-    def test_black(self) -> None:
-        source, expected = read_data("../black")
+    def test_empty(self) -> None:
+        source = expected = ""

         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, line_length=ll)
-        self.assertFalse(ff(THIS_DIR / ".." / "black.py"))
+        black.assert_stable(source, actual, DEFAULT_MODE)

 
 

-    def test_piping(self) -> None:
-        source, expected = read_data("../black")
-        hold_stdin, hold_stdout = sys.stdin, sys.stdout
+    def test_empty_ff(self) -> None:
+        expected = ""
+        tmp_file = Path(black.dump_to_file())

         try:
         try:

-            sys.stdin, sys.stdout = StringIO(source), StringIO()
-            sys.stdin.name = "<stdin>"
-            black.format_stdin_to_stdout(
-                line_length=ll, fast=True, write_back=black.WriteBack.YES
-            )
-            sys.stdout.seek(0)
-            actual = sys.stdout.read()
+            self.assertFalse(ff(tmp_file, write_back=black.WriteBack.YES))
+            with open(tmp_file, encoding="utf8") as f:
+                actual = f.read()

         finally:
         finally:

-            sys.stdin, sys.stdout = hold_stdin, hold_stdout
+            os.unlink(tmp_file)

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

-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, line_length=ll)
+
+    def test_piping(self) -> None:
+        source, expected = read_data("src/black/__init__", data=False)
+        result = BlackRunner().invoke(
+            black.main,
+            ["-", "--fast", f"--line-length={black.DEFAULT_LINE_LENGTH}"],
+            input=BytesIO(source.encode("utf8")),
+        )
+        self.assertEqual(result.exit_code, 0)
+        self.assertFormatEqual(expected, result.output)
+        black.assert_equivalent(source, result.output)
+        black.assert_stable(source, result.output, DEFAULT_MODE)

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

+        diff_header = re.compile(
+            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")

-        hold_stdin, hold_stdout = sys.stdin, sys.stdout
-        try:
-            sys.stdin, sys.stdout = StringIO(source), StringIO()
-            sys.stdin.name = "<stdin>"
-            black.format_stdin_to_stdout(
-                line_length=ll, fast=True, write_back=black.WriteBack.DIFF
-            )
-            sys.stdout.seek(0)
-            actual = sys.stdout.read()
-        finally:
-            sys.stdin, sys.stdout = hold_stdin, hold_stdout
+        config = THIS_DIR / "data" / "empty_pyproject.toml"
+        args = [
+            "-",
+            "--fast",
+            f"--line-length={black.DEFAULT_LINE_LENGTH}",
+            "--diff",
+            f"--config={config}",
+        ]
+        result = BlackRunner().invoke(
+            black.main, args, input=BytesIO(source.encode("utf8"))
+        )
+        self.assertEqual(result.exit_code, 0)
+        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")
-        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)
         self.assertFormatEqual(expected, actual)
         black.assert_equivalent(source, actual)

-        black.assert_stable(source, actual, line_length=ll)
-        self.assertFalse(ff(THIS_DIR / ".." / "setup.py"))
+        black.assert_stable(source, actual, black.FileMode())

 
 

+    @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)
+        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)
+    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_trailing_comma_optional_parens_stability1_pass2(self) -> None:
+        source, _expected = read_data("trailing_comma_optional_parens1")
+        actual = fs(fs(source))  # this is what `format_file_contents` does with --safe
+        black.assert_stable(source, actual, DEFAULT_MODE)
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_trailing_comma_optional_parens_stability2_pass2(self) -> None:
+        source, _expected = read_data("trailing_comma_optional_parens2")
+        actual = fs(fs(source))  # this is what `format_file_contents` does with --safe
+        black.assert_stable(source, actual, DEFAULT_MODE)
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_trailing_comma_optional_parens_stability3_pass2(self) -> None:
+        source, _expected = read_data("trailing_comma_optional_parens3")
+        actual = fs(fs(source))  # this is what `format_file_contents` does with --safe
+        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, line_length=ll)
+        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, line_length=ll)
+        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)
+    def test_pep_572_do_not_remove_parens(self) -> None:
+        source, expected = read_data("pep_572_do_not_remove_parens")
+        # the AST safety checks will fail, but that's expected, just make sure no
+        # parentheses are touched
+        actual = black.format_str(source, mode=DEFAULT_MODE)
+        self.assertFormatEqual(expected, 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")


@@ -187,130 +319,270 @@ 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, line_length=ll)
+            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))
         expected, _ = read_data("expression.diff")
         tmp_file = Path(black.dump_to_file(source))

-        hold_stdout = sys.stdout
+        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:
         try:

-            sys.stdout = StringIO()
-            self.assertTrue(ff(tmp_file, write_back=black.WriteBack.DIFF))
-            sys.stdout.seek(0)
-            actual = sys.stdout.read()
-            actual = actual.replace(tmp_file.name, "<stdin>")
+            result = BlackRunner().invoke(
+                black.main, ["--diff", str(tmp_file), f"--config={config}"]
+            )
+            self.assertEqual(result.exit_code, 0)

         finally:
         finally:

-            sys.stdout = hold_stdout

             os.unlink(tmp_file)
             os.unlink(tmp_file)

-        actual = actual.rstrip() + "\n"  # the diff output has a trailing space
+        actual = result.output
+        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/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, line_length=ll)
+        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:
         source, expected = read_data("string_quotes")
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_string_quotes(self) -> None:
         source, expected = read_data("string_quotes")

-        actual = fs(source)
+        mode = black.Mode(experimental_string_processing=True)
+        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, line_length=ll)
+        black.assert_stable(source, actual, mode)
+        mode = replace(mode, string_normalization=False)
+        not_normalized = fs(source, mode=mode)
+        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)
 
     @patch("black.dump_to_file", dump_to_stderr)

-    def test_comments(self) -> None:
-        source, expected = read_data("comments")
-        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, line_length=ll)
+        black.assert_stable(source, actual, mode)

 
 

-    @patch("black.dump_to_file", dump_to_stderr)
-    def test_comments2(self) -> None:
-        source, expected = read_data("comments2")
-        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, line_length=ll)
+        black.assert_stable(expected, actual, mode)

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

-    def test_comments3(self) -> None:
-        source, expected = read_data("comments3")
-        actual = fs(source)
+    def test_numeric_literals(self) -> None:
+        source, expected = read_data("numeric_literals")
+        mode = replace(DEFAULT_MODE, target_versions=PY36_VERSIONS)
+        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, line_length=ll)
+        black.assert_stable(source, actual, mode)

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

-    def test_comments4(self) -> None:
-        source, expected = read_data("comments4")
-        actual = fs(source)
+    def test_numeric_literals_ignoring_underscores(self) -> None:
+        source, expected = read_data("numeric_literals_skip_underscores")
+        mode = replace(DEFAULT_MODE, target_versions=PY36_VERSIONS)
+        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, line_length=ll)
+        black.assert_stable(source, actual, mode)
+
+    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)

 
 

+    @pytest.mark.no_python2
+    def test_python2_should_fail_without_optional_install(self) -> None:
+        if sys.version_info < (3, 8):
+            self.skipTest(
+                "Python 3.6 and 3.7 will install typed-ast to work and as such will be"
+                " able to parse Python 2 syntax without explicitly specifying the"
+                " python2 extra"
+            )
+
+        source = "x = 1234l"
+        tmp_file = Path(black.dump_to_file(source))
+        try:
+            runner = BlackRunner()
+            result = runner.invoke(black.main, [str(tmp_file)])
+            self.assertEqual(result.exit_code, 123)
+        finally:
+            os.unlink(tmp_file)
+        actual = (
+            runner.stderr_bytes.decode()
+            .replace("\n", "")
+            .replace("\\n", "")
+            .replace("\\r", "")
+            .replace("\r", "")
+        )
+        msg = (
+            "The requested source code has invalid Python 3 syntax."
+            "If you are trying to format Python 2 files please reinstall Black"
+            " with the 'python2' extra: `python3 -m pip install black[python2]`."
+        )
+        self.assertIn(msg, actual)
+
+    @pytest.mark.python2

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

-    def test_cantfit(self) -> None:
-        source, expected = read_data("cantfit")
-        actual = fs(source)
+    def test_python2_print_function(self) -> None:
+        source, expected = read_data("python2_print_function")
+        mode = replace(DEFAULT_MODE, target_versions={TargetVersion.PY27})
+        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, line_length=ll)
+        black.assert_stable(source, actual, mode)

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

-    def test_import_spacing(self) -> None:
-        source, expected = read_data("import_spacing")
-        actual = fs(source)
+    def test_stub(self) -> None:
+        mode = replace(DEFAULT_MODE, is_pyi=True)
+        source, expected = read_data("stub.pyi")
+        actual = fs(source, mode=mode)

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

-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, line_length=ll)
+        black.assert_stable(source, actual, mode)

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

-    def test_composition(self) -> None:
-        source, expected = read_data("composition")
+    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)
         actual = fs(source)
         self.assertFormatEqual(expected, actual)

-        black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, line_length=ll)
+        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 3.6
+        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_empty_lines(self) -> None:
-        source, expected = read_data("empty_lines")
+    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, line_length=ll)
+        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_python2(self) -> None:
-        source, expected = read_data("python2")
+    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, line_length=ll)
+        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_fmtonoff(self) -> None:
-        source, expected = read_data("fmtonoff")
+    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, line_length=ll)
-
-    def test_report(self) -> None:
-        report = black.Report()
+        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"
+        contents_spc = "if 1:\n    if 2:\n        pass\n    # comment\n    pass\n"
+        self.assertFormatEqual(contents_spc, fs(contents_spc))
+        self.assertFormatEqual(contents_spc, fs(contents_tab))
+
+        contents_tab = "if 1:\n\tif 2:\n\t\tpass\n\t\t# comment\n\tpass\n"
+        contents_spc = "if 1:\n    if 2:\n        pass\n        # comment\n    pass\n"
+        self.assertFormatEqual(contents_spc, fs(contents_spc))
+        self.assertFormatEqual(contents_spc, fs(contents_tab))
+
+        # mixed tabs and spaces (valid Python 2 code)
+        contents_tab = "if 1:\n        if 2:\n\t\tpass\n\t# comment\n        pass\n"
+        contents_spc = "if 1:\n    if 2:\n        pass\n    # comment\n    pass\n"
+        self.assertFormatEqual(contents_spc, fs(contents_spc))
+        self.assertFormatEqual(contents_spc, fs(contents_tab))
+
+        contents_tab = "if 1:\n        if 2:\n\t\tpass\n\t\t# comment\n        pass\n"
+        contents_spc = "if 1:\n    if 2:\n        pass\n        # comment\n    pass\n"
+        self.assertFormatEqual(contents_spc, fs(contents_spc))
+        self.assertFormatEqual(contents_spc, fs(contents_tab))
+
+    def test_report_verbose(self) -> None:
+        report = black.Report(verbose=True)

         out_lines = []
         err_lines = []
 
         out_lines = []
         err_lines = []
 


@@ -353,8 +625,8 @@ 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)


@@ -363,8 +635,8 @@ 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")


@@ -373,44 +645,353 @@ 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)
             )
             self.assertEqual(report.return_code, 123)

-            report.done(Path("f4"), black.Changed.NO)
+            report.path_ignored(Path("wat"), "no match")

             self.assertEqual(len(out_lines), 5)
             self.assertEqual(len(err_lines), 2)
             self.assertEqual(len(out_lines), 5)
             self.assertEqual(len(err_lines), 2)

+            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.",
+            )
+            self.assertEqual(report.return_code, 123)
+            report.done(Path("f4"), black.Changed.NO)
+            self.assertEqual(len(out_lines), 6)
+            self.assertEqual(len(err_lines), 2)

             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)),
+                "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:
+        report = black.Report(quiet=True)
+        out_lines = []
+        err_lines = []
+
+        def out(msg: str, **kwargs: Any) -> None:
+            out_lines.append(msg)
+
+        def err(msg: str, **kwargs: Any) -> None:
+            err_lines.append(msg)
+
+        with patch("black.out", out), patch("black.err", err):
+            report.done(Path("f1"), black.Changed.NO)
+            self.assertEqual(len(out_lines), 0)
+            self.assertEqual(len(err_lines), 0)
+            self.assertEqual(unstyle(str(report)), "1 file left unchanged.")
+            self.assertEqual(report.return_code, 0)
+            report.done(Path("f2"), black.Changed.YES)
+            self.assertEqual(len(out_lines), 0)
+            self.assertEqual(len(err_lines), 0)
+            self.assertEqual(
+                unstyle(str(report)), "1 file reformatted, 1 file left unchanged."
+            )
+            report.done(Path("f3"), black.Changed.CACHED)
+            self.assertEqual(len(out_lines), 0)
+            self.assertEqual(len(err_lines), 0)
+            self.assertEqual(
+                unstyle(str(report)), "1 file reformatted, 2 files left unchanged."
+            )
+            self.assertEqual(report.return_code, 0)
+            report.check = True
+            self.assertEqual(report.return_code, 1)
+            report.check = False
+            report.failed(Path("e1"), "boom")
+            self.assertEqual(len(out_lines), 0)
+            self.assertEqual(len(err_lines), 1)
+            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.",
+            )
+            self.assertEqual(report.return_code, 123)
+            report.done(Path("f3"), black.Changed.YES)
+            self.assertEqual(len(out_lines), 0)
+            self.assertEqual(len(err_lines), 1)
+            self.assertEqual(
+                unstyle(str(report)),
+                "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(len(out_lines), 0)
+            self.assertEqual(len(err_lines), 2)
+            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.",
+            )
+            self.assertEqual(report.return_code, 123)
+            report.path_ignored(Path("wat"), "no match")
+            self.assertEqual(len(out_lines), 0)
+            self.assertEqual(len(err_lines), 2)
+            self.assertEqual(
+                unstyle(str(report)),
+                "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(len(out_lines), 0)
+            self.assertEqual(len(err_lines), 2)
+            self.assertEqual(
+                unstyle(str(report)),
+                "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)),
+                "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:
+        report = black.Report()
+        out_lines = []
+        err_lines = []
+
+        def out(msg: str, **kwargs: Any) -> None:
+            out_lines.append(msg)
+
+        def err(msg: str, **kwargs: Any) -> None:
+            err_lines.append(msg)
+
+        with patch("black.out", out), patch("black.err", err):
+            report.done(Path("f1"), black.Changed.NO)
+            self.assertEqual(len(out_lines), 0)
+            self.assertEqual(len(err_lines), 0)
+            self.assertEqual(unstyle(str(report)), "1 file left unchanged.")
+            self.assertEqual(report.return_code, 0)
+            report.done(Path("f2"), black.Changed.YES)
+            self.assertEqual(len(out_lines), 1)
+            self.assertEqual(len(err_lines), 0)
+            self.assertEqual(out_lines[-1], "reformatted f2")
+            self.assertEqual(
+                unstyle(str(report)), "1 file reformatted, 1 file left unchanged."
+            )
+            report.done(Path("f3"), black.Changed.CACHED)
+            self.assertEqual(len(out_lines), 1)
+            self.assertEqual(len(err_lines), 0)
+            self.assertEqual(out_lines[-1], "reformatted f2")
+            self.assertEqual(
+                unstyle(str(report)), "1 file reformatted, 2 files left unchanged."
+            )
+            self.assertEqual(report.return_code, 0)
+            report.check = True
+            self.assertEqual(report.return_code, 1)
+            report.check = False
+            report.failed(Path("e1"), "boom")
+            self.assertEqual(len(out_lines), 1)
+            self.assertEqual(len(err_lines), 1)
+            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.",
+            )
+            self.assertEqual(report.return_code, 123)
+            report.done(Path("f3"), black.Changed.YES)
+            self.assertEqual(len(out_lines), 2)
+            self.assertEqual(len(err_lines), 1)
+            self.assertEqual(out_lines[-1], "reformatted f3")
+            self.assertEqual(
+                unstyle(str(report)),
+                "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(len(out_lines), 2)
+            self.assertEqual(len(err_lines), 2)
+            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.",
+            )
+            self.assertEqual(report.return_code, 123)
+            report.path_ignored(Path("wat"), "no match")
+            self.assertEqual(len(out_lines), 2)
+            self.assertEqual(len(err_lines), 2)
+            self.assertEqual(
+                unstyle(str(report)),
+                "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(len(out_lines), 2)
+            self.assertEqual(len(err_lines), 2)
+            self.assertEqual(
+                unstyle(str(report)),
+                "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:
+        with self.assertRaises(black.InvalidInput):
+            black.lib2to3_parse("invalid syntax")
+
+        straddling = "x + y"
+        black.lib2to3_parse(straddling)
+        black.lib2to3_parse(straddling, {TargetVersion.PY27})
+        black.lib2to3_parse(straddling, {TargetVersion.PY36})
+        black.lib2to3_parse(straddling, {TargetVersion.PY27, TargetVersion.PY36})
+
+        py2_only = "print x"
+        black.lib2to3_parse(py2_only)
+        black.lib2to3_parse(py2_only, {TargetVersion.PY27})
+        with self.assertRaises(black.InvalidInput):
+            black.lib2to3_parse(py2_only, {TargetVersion.PY36})
+        with self.assertRaises(black.InvalidInput):
+            black.lib2to3_parse(py2_only, {TargetVersion.PY27, TargetVersion.PY36})
+
+        py3_only = "exec(x, end=y)"
+        black.lib2to3_parse(py3_only)
+        with self.assertRaises(black.InvalidInput):
+            black.lib2to3_parse(py3_only, {TargetVersion.PY27})
+        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_is_python36(self) -> None:
+    def test_get_features_used(self) -> None:

         node = black.lib2to3_parse("def f(*, arg): ...\n")
         node = black.lib2to3_parse("def f(*, arg): ...\n")

-        self.assertFalse(black.is_python36(node))
+        self.assertEqual(black.get_features_used(node), set())

         node = black.lib2to3_parse("def f(*, arg,): ...\n")
         node = black.lib2to3_parse("def f(*, arg,): ...\n")

-        self.assertTrue(black.is_python36(node))
+        self.assertEqual(black.get_features_used(node), {Feature.TRAILING_COMMA_IN_DEF})
+        node = black.lib2to3_parse("f(*arg,)\n")
+        self.assertEqual(
+            black.get_features_used(node), {Feature.TRAILING_COMMA_IN_CALL}
+        )

         node = black.lib2to3_parse("def f(*, arg): f'string'\n")
         node = black.lib2to3_parse("def f(*, arg): f'string'\n")

-        self.assertTrue(black.is_python36(node))
+        self.assertEqual(black.get_features_used(node), {Feature.F_STRINGS})
+        node = black.lib2to3_parse("123_456\n")
+        self.assertEqual(black.get_features_used(node), {Feature.NUMERIC_UNDERSCORES})
+        node = black.lib2to3_parse("123456\n")
+        self.assertEqual(black.get_features_used(node), set())

         source, expected = read_data("function")
         node = black.lib2to3_parse(source)
         source, expected = read_data("function")
         node = black.lib2to3_parse(source)

-        self.assertTrue(black.is_python36(node))
+        expected_features = {
+            Feature.TRAILING_COMMA_IN_CALL,
+            Feature.TRAILING_COMMA_IN_DEF,
+            Feature.F_STRINGS,
+        }
+        self.assertEqual(black.get_features_used(node), expected_features)

         node = black.lib2to3_parse(expected)
         node = black.lib2to3_parse(expected)

-        self.assertTrue(black.is_python36(node))
+        self.assertEqual(black.get_features_used(node), expected_features)

         source, expected = read_data("expression")
         node = black.lib2to3_parse(source)
         source, expected = read_data("expression")
         node = black.lib2to3_parse(source)

-        self.assertFalse(black.is_python36(node))
+        self.assertEqual(black.get_features_used(node), set())

         node = black.lib2to3_parse(expected)
         node = black.lib2to3_parse(expected)

-        self.assertFalse(black.is_python36(node))
+        self.assertEqual(black.get_features_used(node), set())
+
+    def test_get_future_imports(self) -> None:
+        node = black.lib2to3_parse("\n")
+        self.assertEqual(set(), black.get_future_imports(node))
+        node = black.lib2to3_parse("from __future__ import black\n")
+        self.assertEqual({"black"}, black.get_future_imports(node))
+        node = black.lib2to3_parse("from __future__ import multiple, imports\n")
+        self.assertEqual({"multiple", "imports"}, black.get_future_imports(node))
+        node = black.lib2to3_parse("from __future__ import (parenthesized, imports)\n")
+        self.assertEqual({"parenthesized", "imports"}, black.get_future_imports(node))
+        node = black.lib2to3_parse(
+            "from __future__ import multiple\nfrom __future__ import imports\n"
+        )
+        self.assertEqual({"multiple", "imports"}, black.get_future_imports(node))
+        node = black.lib2to3_parse("# comment\nfrom __future__ import black\n")
+        self.assertEqual({"black"}, black.get_future_imports(node))
+        node = black.lib2to3_parse('"""docstring"""\nfrom __future__ import black\n')
+        self.assertEqual({"black"}, black.get_future_imports(node))
+        node = black.lib2to3_parse("some(other, code)\nfrom __future__ import black\n")
+        self.assertEqual(set(), black.get_future_imports(node))
+        node = black.lib2to3_parse("from some.module import black\n")
+        self.assertEqual(set(), black.get_future_imports(node))
+        node = black.lib2to3_parse(
+            "from __future__ import unicode_literals as _unicode_literals"
+        )
+        self.assertEqual({"unicode_literals"}, black.get_future_imports(node))
+        node = black.lib2to3_parse(
+            "from __future__ import unicode_literals as _lol, print"
+        )
+        self.assertEqual({"unicode_literals", "print"}, black.get_future_imports(node))

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


@@ -438,21 +1019,22 @@ class BlackTestCase(unittest.TestCase):
 
     def test_format_file_contents(self) -> None:
         empty = ""
 
     def test_format_file_contents(self) -> None:
         empty = ""

+        mode = DEFAULT_MODE

         with self.assertRaises(black.NothingChanged):
         with self.assertRaises(black.NothingChanged):

-            black.format_file_contents(empty, line_length=ll, fast=False)
+            black.format_file_contents(empty, mode=mode, fast=False)

         just_nl = "\n"
         with self.assertRaises(black.NothingChanged):
         just_nl = "\n"
         with self.assertRaises(black.NothingChanged):

-            black.format_file_contents(just_nl, line_length=ll, fast=False)
-        same = "l = [1, 2, 3]\n"
+            black.format_file_contents(just_nl, mode=mode, fast=False)
+        same = "j = [1, 2, 3]\n"

         with self.assertRaises(black.NothingChanged):
         with self.assertRaises(black.NothingChanged):

-            black.format_file_contents(same, line_length=ll, fast=False)
-        different = "l = [1,2,3]"
+            black.format_file_contents(same, mode=mode, fast=False)
+        different = "j = [1,2,3]"

         expected = same
         expected = same

-        actual = black.format_file_contents(different, line_length=ll, fast=False)
+        actual = black.format_file_contents(different, mode=mode, fast=False)

         self.assertEqual(expected, actual)
         invalid = "return if you can"
         self.assertEqual(expected, actual)
         invalid = "return if you can"

-        with self.assertRaises(ValueError) as e:
-            black.format_file_contents(invalid, line_length=ll, fast=False)
+        with self.assertRaises(black.InvalidInput) as e:
+            black.format_file_contents(invalid, mode=mode, fast=False)

         self.assertEqual(str(e.exception), "Cannot parse: 1:7: return if you can")
 
     def test_endmarker(self) -> None:
         self.assertEqual(str(e.exception), "Cannot parse: 1:7: return if you can")
 
     def test_endmarker(self) -> None:


@@ -474,7 +1056,7 @@ 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)


@@ -482,76 +1064,132 @@ 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 = DEFAULT_MODE

         with cache_dir() as workspace:
         with cache_dir() as workspace:

-            with black.CACHE_FILE.open("w") as fobj:
+            cache_file = black.get_cache_file(mode)
+            with cache_file.open("w") as fobj:

                 fobj.write("this is not a pickle")
                 fobj.write("this is not a pickle")

-            self.assertEqual(black.read_cache(), {})
+            self.assertEqual(black.read_cache(mode), {})

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

-            result = CliRunner().invoke(black.main, [str(src)])
-            self.assertEqual(result.exit_code, 0)
-            cache = black.read_cache()
-            self.assertIn(src, cache)
+            self.invokeBlack([str(src)])
+            cache = black.read_cache(mode)
+            self.assertIn(str(src), cache)

 
     def test_cache_single_file_already_cached(self) -> None:
 
     def test_cache_single_file_already_cached(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 cache_dir() as workspace:
             src = (workspace / "test.py").resolve()
             with src.open("w") as fobj:
                 fobj.write("print('hello')")

-            black.write_cache({}, [src])
-            result = CliRunner().invoke(black.main, [str(src)])
-            self.assertEqual(result.exit_code, 0)
+            black.write_cache({}, [src], mode)
+            self.invokeBlack([str(src)])

             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:

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

             one = (workspace / "one.py").resolve()
             with one.open("w") as fobj:
                 fobj.write("print('hello')")
             two = (workspace / "two.py").resolve()
             with two.open("w") as fobj:
                 fobj.write("print('hello')")
             one = (workspace / "one.py").resolve()
             with one.open("w") as fobj:
                 fobj.write("print('hello')")
             two = (workspace / "two.py").resolve()
             with two.open("w") as fobj:
                 fobj.write("print('hello')")

-            black.write_cache({}, [one])
-            result = CliRunner().invoke(black.main, [str(workspace)])
-            self.assertEqual(result.exit_code, 0)
+            black.write_cache({}, [one], mode)
+            self.invokeBlack([str(workspace)])

             with one.open("r") as fobj:
                 self.assertEqual(fobj.read(), "print('hello')")
             with two.open("r") as fobj:
                 self.assertEqual(fobj.read(), 'print("hello")\n')
             with one.open("r") as fobj:
                 self.assertEqual(fobj.read(), "print('hello')")
             with two.open("r") as fobj:
                 self.assertEqual(fobj.read(), 'print("hello")\n')

-            cache = black.read_cache()
-            self.assertIn(one, cache)
-            self.assertIn(two, cache)
+            cache = black.read_cache(mode)
+            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 = 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')")

-            result = CliRunner().invoke(black.main, [str(src), "--diff"])
-            self.assertEqual(result.exit_code, 0)
-            self.assertFalse(black.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 = DEFAULT_MODE

         with cache_dir():
         with cache_dir():

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

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

-            self.assertFalse(black.CACHE_FILE.exists())
+            cache_file = black.get_cache_file(mode)
+            self.assertFalse(cache_file.exists())

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

+        mode = DEFAULT_MODE

         with cache_dir():
         with cache_dir():

-            self.assertEqual(black.read_cache(), {})
+            self.assertEqual(black.read_cache(mode), {})

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

+        mode = DEFAULT_MODE

         with cache_dir() as workspace:
             src = (workspace / "test.py").resolve()
             src.touch()
         with cache_dir() as workspace:
             src = (workspace / "test.py").resolve()
             src.touch()

-            black.write_cache({}, [src])
-            cache = black.read_cache()
-            self.assertIn(src, cache)
-            self.assertEqual(cache[src], black.get_cache_info(src))
+            black.write_cache({}, [src], mode)
+            cache = black.read_cache(mode)
+            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:


@@ -562,57 +1200,885 @@ 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(
             todo, done = black.filter_cached(

-                cache, [uncached, cached, cached_but_changed]
+                cache, {uncached, cached, cached_but_changed}

             )
             )

-            self.assertEqual(todo, [uncached, cached_but_changed])
-            self.assertEqual(done, [cached])
+            self.assertEqual(todo, {uncached, cached_but_changed})
+            self.assertEqual(done, {cached})

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

+        mode = DEFAULT_MODE

         with cache_dir(exists=False) as workspace:
             self.assertFalse(workspace.exists())
         with cache_dir(exists=False) as workspace:
             self.assertFalse(workspace.exists())

-            black.write_cache({}, [])
+            black.write_cache({}, [], mode)

             self.assertTrue(workspace.exists())
 
             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:

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

             failing = (workspace / "failing.py").resolve()
             with failing.open("w") as fobj:
                 fobj.write("not actually python")
             clean = (workspace / "clean.py").resolve()
             with clean.open("w") as fobj:
                 fobj.write('print("hello")\n')
             failing = (workspace / "failing.py").resolve()
             with failing.open("w") as fobj:
                 fobj.write("not actually python")
             clean = (workspace / "clean.py").resolve()
             with clean.open("w") as fobj:
                 fobj.write('print("hello")\n')

-            result = CliRunner().invoke(black.main, [str(workspace)])
-            self.assertEqual(result.exit_code, 123)
-            cache = black.read_cache()
-            self.assertNotIn(failing, cache)
-            self.assertIn(clean, cache)
+            self.invokeBlack([str(workspace)], exit_code=123)
+            cache = black.read_cache(mode)
+            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 = DEFAULT_MODE

         with cache_dir(), patch.object(Path, "open") as mock:
             mock.side_effect = OSError
         with cache_dir(), patch.object(Path, "open") as mock:
             mock.side_effect = OSError

-            black.write_cache({}, [])
+            black.write_cache({}, [], mode)

 
 

+    @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.

-            src1 = (THIS_DIR / "string_quotes.py").resolve()
-            result = CliRunner().invoke(black.main, [str(src1), "--diff", "--check"])
-            self.assertEqual(result.exit_code, 1)
-
+            src1 = (THIS_DIR / "data" / "string_quotes.py").resolve()
+            self.invokeBlack([str(src1), "--diff", "--check"], exit_code=1)

             # Files which will not be reformatted.
             # Files which will not be reformatted.

-            src2 = (THIS_DIR / "composition.py").resolve()
-            result = CliRunner().invoke(black.main, [str(src2), "--diff", "--check"])
+            src2 = (THIS_DIR / "data" / "composition.py").resolve()
+            self.invokeBlack([str(src2), "--diff", "--check"])
+            # Multi file command.
+            self.invokeBlack([str(src1), str(src2), "--diff", "--check"], exit_code=1)
+
+    def test_no_files(self) -> None:
+        with cache_dir():
+            # Without an argument, black exits with error code 0.
+            self.invokeBlack([])
+
+    def test_broken_symlink(self) -> None:
+        with cache_dir() as workspace:
+            symlink = workspace / "broken_link.py"
+            try:
+                symlink.symlink_to("nonexistent.py")
+            except OSError as e:
+                self.skipTest(f"Can't create symlinks: {e}")
+            self.invokeBlack([str(workspace.resolve())])
+
+    def test_read_cache_line_lengths(self) -> None:
+        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)
+            self.assertIn(str(path), one)
+            two = black.read_cache(short_mode)
+            self.assertNotIn(str(path), two)
+
+    def test_single_file_force_pyi(self) -> None:
+        pyi_mode = replace(DEFAULT_MODE, is_pyi=True)
+        contents, expected = read_data("force_pyi")
+        with cache_dir() as workspace:
+            path = (workspace / "file.py").resolve()
+            with open(path, "w") as fh:
+                fh.write(contents)
+            self.invokeBlack([str(path), "--pyi"])
+            with open(path, "r") as fh:
+                actual = fh.read()
+            # verify cache with --pyi is separate
+            pyi_cache = black.read_cache(pyi_mode)
+            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()
+    def test_multi_file_force_pyi(self) -> None:
+        reg_mode = DEFAULT_MODE
+        pyi_mode = replace(DEFAULT_MODE, is_pyi=True)
+        contents, expected = read_data("force_pyi")
+        with cache_dir() as workspace:
+            paths = [
+                (workspace / "file1.py").resolve(),
+                (workspace / "file2.py").resolve(),
+            ]
+            for path in paths:
+                with open(path, "w") as fh:
+                    fh.write(contents)
+            self.invokeBlack([str(p) for p in paths] + ["--pyi"])
+            for path in paths:
+                with open(path, "r") as fh:
+                    actual = fh.read()
+                self.assertEqual(actual, expected)
+            # verify cache with --pyi is separate
+            pyi_cache = black.read_cache(pyi_mode)
+            normal_cache = black.read_cache(reg_mode)
+            for path in paths:
+                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")
+        result = CliRunner().invoke(
+            black.main, ["-", "-q", "--pyi"], input=BytesIO(source.encode("utf8"))
+        )
+        self.assertEqual(result.exit_code, 0)
+        actual = result.output
+        self.assertFormatEqual(actual, expected)
+
+    def test_single_file_force_py36(self) -> None:
+        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()
+            with open(path, "w") as fh:
+                fh.write(source)
+            self.invokeBlack([str(path), *PY36_ARGS])
+            with open(path, "r") as fh:
+                actual = fh.read()
+            # verify cache with --target-version is separate
+            py36_cache = black.read_cache(py36_mode)
+            self.assertIn(str(path), py36_cache)
+            normal_cache = black.read_cache(reg_mode)
+            self.assertNotIn(str(path), normal_cache)
+        self.assertEqual(actual, expected)
+
+    @event_loop()
+    def test_multi_file_force_py36(self) -> None:
+        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 = [
+                (workspace / "file1.py").resolve(),
+                (workspace / "file2.py").resolve(),
+            ]
+            for path in paths:
+                with open(path, "w") as fh:
+                    fh.write(source)
+            self.invokeBlack([str(p) for p in paths] + PY36_ARGS)
+            for path in paths:
+                with open(path, "r") as fh:
+                    actual = fh.read()
+                self.assertEqual(actual, expected)
+            # verify cache with --target-version is separate
+            pyi_cache = black.read_cache(py36_mode)
+            normal_cache = black.read_cache(reg_mode)
+            for path in paths:
+                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")
+        result = CliRunner().invoke(
+            black.main,
+            ["-", "-q", "--target-version=py36"],
+            input=BytesIO(source.encode("utf8")),
+        )
+        self.assertEqual(result.exit_code, 0)
+        actual = result.output
+        self.assertFormatEqual(actual, expected)
+
+    def test_include_exclude(self) -> None:
+        path = THIS_DIR / "data" / "include_exclude_tests"
+        include = re.compile(r"\.pyi?$")
+        exclude = re.compile(r"/exclude/|/\.definitely_exclude/")
+        report = black.Report()
+        gitignore = PathSpec.from_lines("gitwildmatch", [])
+        sources: List[Path] = []
+        expected = [
+            Path(path / "b/dont_exclude/a.py"),
+            Path(path / "b/dont_exclude/a.pyi"),
+        ]
+        this_abs = THIS_DIR.resolve()
+        sources.extend(
+            black.gen_python_files(
+                path.iterdir(),
+                this_abs,
+                include,
+                exclude,
+                None,
+                None,
+                report,
+                gitignore,
+            )
+        )
+        self.assertEqual(sorted(expected), sorted(sources))
+
+    def test_gitingore_used_as_default(self) -> None:
+        path = Path(THIS_DIR / "data" / "include_exclude_tests")
+        include = re.compile(r"\.pyi?$")
+        extend_exclude = re.compile(r"/exclude/")
+        src = str(path / "b/")
+        report = black.Report()
+        expected: List[Path] = [
+            path / "b/.definitely_exclude/a.py",
+            path / "b/.definitely_exclude/a.pyi",
+        ]
+        sources = list(
+            black.get_sources(
+                ctx=FakeContext(),
+                src=(src,),
+                quiet=True,
+                verbose=False,
+                include=include,
+                exclude=None,
+                extend_exclude=extend_exclude,
+                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_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_with(
+                fast=True, write_back=black.WriteBack.YES, mode=DEFAULT_MODE
+            )
+            # __BLACK_STDIN_FILENAME__ should have been stripped
+            report.done.assert_called_with(expected, black.Changed.YES)
+
+    def test_reformat_one_with_stdin_filename_pyi(self) -> None:
+        with patch(
+            "black.format_stdin_to_stdout",
+            return_value=lambda *args, **kwargs: black.Changed.YES,
+        ) as fsts:
+            report = MagicMock()
+            p = "foo.pyi"
+            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_with(
+                fast=True,
+                write_back=black.WriteBack.YES,
+                mode=replace(DEFAULT_MODE, is_pyi=True),
+            )
+            # __BLACK_STDIN_FILENAME__ should have been stripped
+            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 stripped
+            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()
+        gitignore = PathSpec.from_lines("gitwildmatch", [])
+        empty = re.compile(r"")
+        sources: List[Path] = []
+        expected = [
+            Path(path / "b/exclude/a.pie"),
+            Path(path / "b/exclude/a.py"),
+            Path(path / "b/exclude/a.pyi"),
+            Path(path / "b/dont_exclude/a.pie"),
+            Path(path / "b/dont_exclude/a.py"),
+            Path(path / "b/dont_exclude/a.pyi"),
+            Path(path / "b/.definitely_exclude/a.pie"),
+            Path(path / "b/.definitely_exclude/a.py"),
+            Path(path / "b/.definitely_exclude/a.pyi"),
+            Path(path / ".gitignore"),
+            Path(path / "pyproject.toml"),
+        ]
+        this_abs = THIS_DIR.resolve()
+        sources.extend(
+            black.gen_python_files(
+                path.iterdir(),
+                this_abs,
+                empty,
+                re.compile(black.DEFAULT_EXCLUDES),
+                None,
+                None,
+                report,
+                gitignore,
+            )
+        )
+        self.assertEqual(sorted(expected), sorted(sources))
+
+    def test_extend_exclude(self) -> None:
+        path = THIS_DIR / "data" / "include_exclude_tests"
+        report = black.Report()
+        gitignore = PathSpec.from_lines("gitwildmatch", [])
+        sources: List[Path] = []
+        expected = [
+            Path(path / "b/exclude/a.py"),
+            Path(path / "b/dont_exclude/a.py"),
+        ]
+        this_abs = THIS_DIR.resolve()
+        sources.extend(
+            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))
+
+    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:
+        with TemporaryDirectory() as workspace:
+            test_file = Path(workspace) / "test.py"
+            for nl in ["\n", "\r\n"]:
+                contents = nl.join(["def f(  ):", "    pass"])
+                test_file.write_bytes(contents.encode())
+                ff(test_file, write_back=black.WriteBack.YES)
+                updated_contents: bytes = test_file.read_bytes()
+                self.assertIn(nl.encode(), updated_contents)
+                if nl == "\n":
+                    self.assertNotIn(b"\r\n", updated_contents)
+
+    def test_preserves_line_endings_via_stdin(self) -> None:
+        for nl in ["\n", "\r\n"]:
+            contents = nl.join(["def f(  ):", "    pass"])
+            runner = BlackRunner()
+            result = runner.invoke(
+                black.main, ["-", "--fast"], input=BytesIO(contents.encode("utf8"))
+            )

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

+            output = runner.stdout_bytes
+            self.assertIn(nl.encode("utf8"), output)
+            if nl == "\n":
+                self.assertNotIn(b"\r\n", output)
+
+    def test_assert_equivalent_different_asts(self) -> None:
+        with self.assertRaises(AssertionError):
+            black.assert_equivalent("{}", "None")
+
+    def test_symlink_out_of_root_directory(self) -> None:
+        path = MagicMock()
+        root = THIS_DIR.resolve()
+        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.as_posix.return_value = "/a/b/c"
+        child.is_symlink.return_value = True
+        try:
+            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()
+        child.resolve.assert_called_once()
+        child.is_symlink.assert_called_once()
+        # `child` should behave like a strange file which resolved path is clearly
+        # outside of the `root` directory.
+        child.is_symlink.return_value = False
+        with self.assertRaises(ValueError):
+            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()
+        self.assertEqual(child.resolve.call_count, 2)
+        child.is_symlink.assert_called()
+        self.assertEqual(child.is_symlink.call_count, 2)
+
+    def test_shhh_click(self) -> None:
+        try:
+            from click import _unicodefun  # type: ignore
+        except ModuleNotFoundError:
+            self.skipTest("Incompatible Click version")
+        if not hasattr(_unicodefun, "_verify_python3_env"):
+            self.skipTest("Incompatible Click version")
+        # First, let's see if Click is crashing with a preferred ASCII charset.
+        with patch("locale.getpreferredencoding") as gpe:
+            gpe.return_value = "ASCII"
+            with self.assertRaises(RuntimeError):
+                _unicodefun._verify_python3_env()
+        # Now, let's silence Click...
+        black.patch_click()
+        # ...and confirm it's silent.
+        with patch("locale.getpreferredencoding") as gpe:
+            gpe.return_value = "ASCII"
+            try:
+                _unicodefun._verify_python3_env()
+            except RuntimeError as re:
+                self.fail(f"`patch_click()` failed, exception still raised: {re}")
+
+    def test_root_logger_not_used_directly(self) -> None:
+        def fail(*args: Any, **kwargs: Any) -> None:
+            self.fail("Record created with root logger")
+
+        with patch.multiple(
+            logging.root,
+            debug=fail,
+            info=fail,
+            warning=fail,
+            error=fail,
+            critical=fail,
+            log=fail,
+        ):
+            ff(THIS_FILE)
+
+    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()

 
 

-            # Multi file command.
-            result = CliRunner().invoke(
-                black.main, [str(src1), str(src2), "--diff", "--check"]
+            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(result.exit_code, 1)
+            self.assertEqual(black.find_project_root((src_dir,)), src_dir.resolve())
+            self.assertEqual(black.find_project_root((src_python,)), src_dir.resolve())
+
+    @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()
+                )
+
+        # 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()
+            )
+
+    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)
+        finally:
+            os.unlink(tmp_file)
+        actual = result.output
+        actual = diff_header.sub(DETERMINISTIC_HEADER, actual)
+        self.assertEqual(actual, expected)
+
+    @pytest.mark.python2
+    def test_docstring_reformat_for_py27(self) -> None:
+        """
+        Check that stripping trailing whitespace from Python 2 docstrings
+        doesn't trigger a "not equivalent to source" error
+        """
+        source = (
+            b'def foo():\r\n    """Testing\r\n    Testing """\r\n    print "Foo"\r\n'
+        )
+        expected = 'def foo():\n    """Testing\n    Testing"""\n    print "Foo"\n'
+
+        result = CliRunner().invoke(
+            black.main,
+            ["-", "-q", "--target-version=py27"],
+            input=BytesIO(source),
+        )
+
+        self.assertEqual(result.exit_code, 0)
+        actual = result.output
+        self.assertFormatEqual(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__":

-    unittest.main()
+    unittest.main(module="test_black")