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Fix async blackd tests which won't fail currently (#966)
[etc/vim.git] / tests / test_black.py
index 421e8712da130d9f592180c7afcd4b2a6ebab833..a465d5456863ea0baf4bc391df82ac448880c869 100644 (file)
@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 import asyncio
+import logging
 from concurrent.futures import ThreadPoolExecutor
 from contextlib import contextmanager
 from functools import partial
@@ -9,7 +10,7 @@ from pathlib import Path
 import re
 import sys
 from tempfile import TemporaryDirectory
-from typing import Any, BinaryIO, Generator, List, Tuple, Iterator
+from typing import Any, BinaryIO, Generator, List, Tuple, Iterator, TypeVar
 import unittest
 from unittest.mock import patch, MagicMock
 
@@ -17,14 +18,27 @@ from click import unstyle
 from click.testing import CliRunner
 
 import black
-
-
-ll = 88
-ff = partial(black.format_file_in_place, line_length=ll, fast=True)
-fs = partial(black.format_str, line_length=ll)
+from black import Feature, TargetVersion
+
+try:
+    import blackd
+    from aiohttp.test_utils import AioHTTPTestCase, unittest_run_loop
+    from aiohttp import web
+except ImportError:
+    has_blackd_deps = False
+else:
+    has_blackd_deps = True
+
+ff = partial(black.format_file_in_place, mode=black.FileMode(), fast=True)
+fs = partial(black.format_str, mode=black.FileMode())
 THIS_FILE = Path(__file__)
 THIS_DIR = THIS_FILE.parent
 EMPTY_LINE = "# EMPTY LINE WITH WHITESPACE" + " (this comment will be removed)"
+PY36_ARGS = [
+    f"--target-version={version.name.lower()}" for version in black.PY36_VERSIONS
+]
+T = TypeVar("T")
+R = TypeVar("R")
 
 
 def dump_to_stderr(*output: str) -> str:
@@ -67,18 +81,27 @@ def cache_dir(exists: bool = True) -> Iterator[Path]:
 @contextmanager
 def event_loop(close: bool) -> Iterator[None]:
     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:
-        policy.set_event_loop(old_loop)
         if close:
             loop.close()
 
 
+@contextmanager
+def skip_if_exception(e: str) -> Iterator[None]:
+    try:
+        yield
+    except Exception as exc:
+        if exc.__class__.__name__ == e:
+            unittest.skip(f"Encountered expected exception {exc}, skipping")
+        else:
+            raise exc
+
+
 class BlackRunner(CliRunner):
     """Modify CliRunner so that stderr is not merged with stdout.
 
@@ -99,8 +122,8 @@ class BlackRunner(CliRunner):
                 sys.stderr = TextIOWrapper(self.stderrbuf, encoding=self.charset)
                 yield output
             finally:
-                self.stdout_bytes = sys.stdout.buffer.getvalue()
-                self.stderr_bytes = sys.stderr.buffer.getvalue()
+                self.stdout_bytes = sys.stdout.buffer.getvalue()  # type: ignore
+                self.stderr_bytes = sys.stderr.buffer.getvalue()  # type: ignore
                 sys.stderr = hold_stderr
 
 
@@ -126,13 +149,22 @@ class BlackTestCase(unittest.TestCase):
                 black.err(str(ve))
         self.assertEqual(expected, actual)
 
+    def invokeBlack(
+        self, args: List[str], exit_code: int = 0, ignore_config: bool = True
+    ) -> None:
+        runner = BlackRunner()
+        if ignore_config:
+            args = ["--config", str(THIS_DIR / "empty.toml"), *args]
+        result = runner.invoke(black.main, args)
+        self.assertEqual(result.exit_code, exit_code, msg=runner.stderr_bytes.decode())
+
     @patch("black.dump_to_file", dump_to_stderr)
     def test_empty(self) -> None:
         source = expected = ""
         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, black.FileMode())
 
     def test_empty_ff(self) -> None:
         expected = ""
@@ -151,7 +183,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
         self.assertFalse(ff(THIS_FILE))
 
     @patch("black.dump_to_file", dump_to_stderr)
@@ -160,20 +192,20 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
         self.assertFalse(ff(THIS_DIR / ".." / "black.py"))
 
     def test_piping(self) -> None:
         source, expected = read_data("../black", data=False)
         result = BlackRunner().invoke(
             black.main,
-            ["-", "--fast", f"--line-length={ll}"],
+            ["-", "--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, line_length=ll)
+        black.assert_stable(source, result.output, black.FileMode())
 
     def test_piping_diff(self) -> None:
         diff_header = re.compile(
@@ -183,7 +215,13 @@ class BlackTestCase(unittest.TestCase):
         source, _ = read_data("expression.py")
         expected, _ = read_data("expression.diff")
         config = THIS_DIR / "data" / "empty_pyproject.toml"
-        args = ["-", "--fast", f"--line-length={ll}", "--diff", f"--config={config}"]
+        args = [
+            "-",
+            "--fast",
+            f"--line-length={black.DEFAULT_LINE_LENGTH}",
+            "--diff",
+            f"--config={config}",
+        ]
         result = BlackRunner().invoke(
             black.main, args, input=BytesIO(source.encode("utf8"))
         )
@@ -198,7 +236,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
         self.assertFalse(ff(THIS_DIR / ".." / "setup.py"))
 
     @patch("black.dump_to_file", dump_to_stderr)
@@ -207,7 +245,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_function2(self) -> None:
@@ -215,7 +253,15 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_function_trailing_comma(self) -> None:
+        source, expected = read_data("function_trailing_comma")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_expression(self) -> None:
@@ -223,7 +269,24 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
+
+    @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)
+        black.assert_stable(source, actual, black.FileMode())
+        if sys.version_info >= (3, 8):
+            black.assert_equivalent(source, actual)
+
+    def test_pep_572_version_detection(self) -> None:
+        source, _ = read_data("pep_572")
+        root = black.lib2to3_parse(source)
+        features = black.get_features_used(root)
+        self.assertIn(black.Feature.ASSIGNMENT_EXPRESSIONS, features)
+        versions = black.detect_target_versions(root)
+        self.assertIn(black.TargetVersion.PY38, versions)
 
     def test_expression_ff(self) -> None:
         source, expected = read_data("expression")
@@ -237,7 +300,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
 
     def test_expression_diff(self) -> None:
         source, _ = read_data("expression.py")
@@ -260,7 +323,7 @@ class BlackTestCase(unittest.TestCase):
             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}"
+                f"overwrite tests/data/expression.diff with {dump}"
             )
             self.assertEqual(expected, actual, msg)
 
@@ -270,7 +333,24 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_pep_570(self) -> None:
+        source, expected = read_data("pep_570")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        black.assert_stable(source, actual, black.FileMode())
+        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:
@@ -278,12 +358,12 @@ class BlackTestCase(unittest.TestCase):
         actual = fs(source)
         self.assertFormatEqual(expected, actual)
         black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, line_length=ll)
-        mode = black.FileMode.NO_STRING_NORMALIZATION
+        black.assert_stable(source, actual, black.FileMode())
+        mode = black.FileMode(string_normalization=False)
         not_normalized = fs(source, mode=mode)
         self.assertFormatEqual(source, not_normalized)
         black.assert_equivalent(source, not_normalized)
-        black.assert_stable(source, not_normalized, line_length=ll, mode=mode)
+        black.assert_stable(source, not_normalized, mode=mode)
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_slices(self) -> None:
@@ -291,7 +371,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_comments(self) -> None:
@@ -299,7 +379,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_comments2(self) -> None:
@@ -307,7 +387,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_comments3(self) -> None:
@@ -315,7 +395,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_comments4(self) -> None:
@@ -323,7 +403,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_comments5(self) -> None:
@@ -331,7 +411,31 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_comments6(self) -> None:
+        source, expected = read_data("comments6")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, black.FileMode())
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_comments7(self) -> None:
+        source, expected = read_data("comments7")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, black.FileMode())
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_comment_after_escaped_newline(self) -> None:
+        source, expected = read_data("comment_after_escaped_newline")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_cantfit(self) -> None:
@@ -339,7 +443,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_import_spacing(self) -> None:
@@ -347,7 +451,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_composition(self) -> None:
@@ -355,7 +459,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_empty_lines(self) -> None:
@@ -363,7 +467,15 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_remove_parens(self) -> None:
+        source, expected = read_data("remove_parens")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_string_prefixes(self) -> None:
@@ -371,55 +483,95 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_numeric_literals(self) -> None:
         source, expected = read_data("numeric_literals")
-        actual = fs(source, mode=black.FileMode.PYTHON36)
+        mode = black.FileMode(target_versions=black.PY36_VERSIONS)
+        actual = fs(source, mode=mode)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, mode)
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_numeric_literals_ignoring_underscores(self) -> None:
+        source, expected = read_data("numeric_literals_skip_underscores")
+        mode = black.FileMode(target_versions=black.PY36_VERSIONS)
+        actual = fs(source, mode=mode)
         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_numeric_literals_py2(self) -> None:
         source, expected = read_data("numeric_literals_py2")
         actual = fs(source)
         self.assertFormatEqual(expected, actual)
-        black.assert_stable(source, actual, line_length=ll)
+        black.assert_stable(source, actual, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_python2(self) -> None:
         source, expected = read_data("python2")
         actual = fs(source)
         self.assertFormatEqual(expected, actual)
-        # black.assert_equivalent(source, actual)
-        black.assert_stable(source, actual, line_length=ll)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, black.FileMode())
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_python2_print_function(self) -> None:
+        source, expected = read_data("python2_print_function")
+        mode = black.FileMode(target_versions={TargetVersion.PY27})
+        actual = fs(source, mode=mode)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, mode)
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_python2_unicode_literals(self) -> None:
         source, expected = read_data("python2_unicode_literals")
         actual = fs(source)
         self.assertFormatEqual(expected, actual)
-        black.assert_stable(source, actual, line_length=ll)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_stub(self) -> None:
-        mode = black.FileMode.PYI
+        mode = black.FileMode(is_pyi=True)
         source, expected = read_data("stub.pyi")
         actual = fs(source, mode=mode)
         self.assertFormatEqual(expected, actual)
-        black.assert_stable(source, actual, line_length=ll, mode=mode)
+        black.assert_stable(source, actual, mode)
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_async_as_identifier(self) -> None:
+        source_path = (THIS_DIR / "data" / "async_as_identifier.py").resolve()
+        source, expected = read_data("async_as_identifier")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        major, minor = sys.version_info[:2]
+        if major < 3 or (major <= 3 and minor < 7):
+            black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, black.FileMode())
+        # 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)
     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)
         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, line_length=ll)
+        black.assert_stable(source, actual, black.FileMode())
+        # 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)
     def test_fmtonoff(self) -> None:
@@ -427,7 +579,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_fmtonoff2(self) -> None:
@@ -435,7 +587,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_remove_empty_parentheses_after_class(self) -> None:
@@ -443,7 +595,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_new_line_between_class_and_code(self) -> None:
@@ -451,7 +603,7 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_bracket_match(self) -> None:
@@ -459,7 +611,45 @@ class BlackTestCase(unittest.TestCase):
         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, black.FileMode())
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_tuple_assign(self) -> None:
+        source, expected = read_data("tupleassign")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, black.FileMode())
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_beginning_backslash(self) -> None:
+        source, expected = read_data("beginning_backslash")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, black.FileMode())
+
+    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)
@@ -733,27 +923,61 @@ class BlackTestCase(unittest.TestCase):
                 "2 files would fail to reformat.",
             )
 
-    def test_is_python36(self) -> None:
+    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(self) -> None:
         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")
-        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")
-        self.assertTrue(black.is_python36(node))
+        self.assertEqual(black.get_features_used(node), {Feature.F_STRINGS})
         node = black.lib2to3_parse("123_456\n")
-        self.assertTrue(black.is_python36(node))
+        self.assertEqual(black.get_features_used(node), {Feature.NUMERIC_UNDERSCORES})
         node = black.lib2to3_parse("123456\n")
-        self.assertFalse(black.is_python36(node))
+        self.assertEqual(black.get_features_used(node), set())
         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)
-        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)
-        self.assertFalse(black.is_python36(node))
+        self.assertEqual(black.get_features_used(node), set())
         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")
@@ -811,21 +1035,22 @@ class BlackTestCase(unittest.TestCase):
 
     def test_format_file_contents(self) -> None:
         empty = ""
+        mode = black.FileMode()
         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):
-            black.format_file_contents(just_nl, line_length=ll, fast=False)
+            black.format_file_contents(just_nl, mode=mode, fast=False)
         same = "l = [1, 2, 3]\n"
         with self.assertRaises(black.NothingChanged):
-            black.format_file_contents(same, line_length=ll, fast=False)
+            black.format_file_contents(same, mode=mode, fast=False)
         different = "l = [1,2,3]"
         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"
-        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:
@@ -855,35 +1080,33 @@ class BlackTestCase(unittest.TestCase):
         self.assertEqual("".join(err_lines), "")
 
     def test_cache_broken_file(self) -> None:
-        mode = black.FileMode.AUTO_DETECT
+        mode = black.FileMode()
         with cache_dir() as workspace:
-            cache_file = black.get_cache_file(black.DEFAULT_LINE_LENGTH, mode)
+            cache_file = black.get_cache_file(mode)
             with cache_file.open("w") as fobj:
                 fobj.write("this is not a pickle")
-            self.assertEqual(black.read_cache(black.DEFAULT_LINE_LENGTH, mode), {})
+            self.assertEqual(black.read_cache(mode), {})
             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(black.DEFAULT_LINE_LENGTH, mode)
+            self.invokeBlack([str(src)])
+            cache = black.read_cache(mode)
             self.assertIn(src, cache)
 
     def test_cache_single_file_already_cached(self) -> None:
-        mode = black.FileMode.AUTO_DETECT
+        mode = black.FileMode()
         with cache_dir() as workspace:
             src = (workspace / "test.py").resolve()
             with src.open("w") as fobj:
                 fobj.write("print('hello')")
-            black.write_cache({}, [src], black.DEFAULT_LINE_LENGTH, mode)
-            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')")
 
     @event_loop(close=False)
     def test_cache_multiple_files(self) -> None:
-        mode = black.FileMode.AUTO_DETECT
+        mode = black.FileMode()
         with cache_dir() as workspace, patch(
             "black.ProcessPoolExecutor", new=ThreadPoolExecutor
         ):
@@ -893,50 +1116,48 @@ class BlackTestCase(unittest.TestCase):
             two = (workspace / "two.py").resolve()
             with two.open("w") as fobj:
                 fobj.write("print('hello')")
-            black.write_cache({}, [one], black.DEFAULT_LINE_LENGTH, mode)
-            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')
-            cache = black.read_cache(black.DEFAULT_LINE_LENGTH, mode)
+            cache = black.read_cache(mode)
             self.assertIn(one, cache)
             self.assertIn(two, cache)
 
     def test_no_cache_when_writeback_diff(self) -> None:
-        mode = black.FileMode.AUTO_DETECT
+        mode = black.FileMode()
         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)
-            cache_file = black.get_cache_file(black.DEFAULT_LINE_LENGTH, mode)
+            self.invokeBlack([str(src), "--diff"])
+            cache_file = black.get_cache_file(mode)
             self.assertFalse(cache_file.exists())
 
     def test_no_cache_when_stdin(self) -> None:
-        mode = black.FileMode.AUTO_DETECT
+        mode = black.FileMode()
         with cache_dir():
             result = CliRunner().invoke(
                 black.main, ["-"], input=BytesIO(b"print('hello')")
             )
             self.assertEqual(result.exit_code, 0)
-            cache_file = black.get_cache_file(black.DEFAULT_LINE_LENGTH, mode)
+            cache_file = black.get_cache_file(mode)
             self.assertFalse(cache_file.exists())
 
     def test_read_cache_no_cachefile(self) -> None:
-        mode = black.FileMode.AUTO_DETECT
+        mode = black.FileMode()
         with cache_dir():
-            self.assertEqual(black.read_cache(black.DEFAULT_LINE_LENGTH, mode), {})
+            self.assertEqual(black.read_cache(mode), {})
 
     def test_write_cache_read_cache(self) -> None:
-        mode = black.FileMode.AUTO_DETECT
+        mode = black.FileMode()
         with cache_dir() as workspace:
             src = (workspace / "test.py").resolve()
             src.touch()
-            black.write_cache({}, [src], black.DEFAULT_LINE_LENGTH, mode)
-            cache = black.read_cache(black.DEFAULT_LINE_LENGTH, mode)
+            black.write_cache({}, [src], mode)
+            cache = black.read_cache(mode)
             self.assertIn(src, cache)
             self.assertEqual(cache[src], black.get_cache_info(src))
 
@@ -957,15 +1178,15 @@ class BlackTestCase(unittest.TestCase):
             self.assertEqual(done, {cached})
 
     def test_write_cache_creates_directory_if_needed(self) -> None:
-        mode = black.FileMode.AUTO_DETECT
+        mode = black.FileMode()
         with cache_dir(exists=False) as workspace:
             self.assertFalse(workspace.exists())
-            black.write_cache({}, [], black.DEFAULT_LINE_LENGTH, mode)
+            black.write_cache({}, [], mode)
             self.assertTrue(workspace.exists())
 
     @event_loop(close=False)
     def test_failed_formatting_does_not_get_cached(self) -> None:
-        mode = black.FileMode.AUTO_DETECT
+        mode = black.FileMode()
         with cache_dir() as workspace, patch(
             "black.ProcessPoolExecutor", new=ThreadPoolExecutor
         ):
@@ -975,40 +1196,33 @@ class BlackTestCase(unittest.TestCase):
             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(black.DEFAULT_LINE_LENGTH, mode)
+            self.invokeBlack([str(workspace)], exit_code=123)
+            cache = black.read_cache(mode)
             self.assertNotIn(failing, cache)
             self.assertIn(clean, cache)
 
     def test_write_cache_write_fail(self) -> None:
-        mode = black.FileMode.AUTO_DETECT
+        mode = black.FileMode()
         with cache_dir(), patch.object(Path, "open") as mock:
             mock.side_effect = OSError
-            black.write_cache({}, [], black.DEFAULT_LINE_LENGTH, mode)
+            black.write_cache({}, [], mode)
 
     @event_loop(close=False)
     def test_check_diff_use_together(self) -> None:
         with cache_dir():
             # Files which will be reformatted.
             src1 = (THIS_DIR / "data" / "string_quotes.py").resolve()
-            result = CliRunner().invoke(black.main, [str(src1), "--diff", "--check"])
-            self.assertEqual(result.exit_code, 1, result.output)
+            self.invokeBlack([str(src1), "--diff", "--check"], exit_code=1)
             # Files which will not be reformatted.
             src2 = (THIS_DIR / "data" / "composition.py").resolve()
-            result = CliRunner().invoke(black.main, [str(src2), "--diff", "--check"])
-            self.assertEqual(result.exit_code, 0, result.output)
+            self.invokeBlack([str(src2), "--diff", "--check"])
             # Multi file command.
-            result = CliRunner().invoke(
-                black.main, [str(src1), str(src2), "--diff", "--check"]
-            )
-            self.assertEqual(result.exit_code, 1, result.output)
+            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.
-            result = CliRunner().invoke(black.main, [])
-            self.assertEqual(result.exit_code, 0)
+            self.invokeBlack([])
 
     def test_broken_symlink(self) -> None:
         with cache_dir() as workspace:
@@ -1017,43 +1231,42 @@ class BlackTestCase(unittest.TestCase):
                 symlink.symlink_to("nonexistent.py")
             except OSError as e:
                 self.skipTest(f"Can't create symlinks: {e}")
-            result = CliRunner().invoke(black.main, [str(workspace.resolve())])
-            self.assertEqual(result.exit_code, 0)
+            self.invokeBlack([str(workspace.resolve())])
 
     def test_read_cache_line_lengths(self) -> None:
-        mode = black.FileMode.AUTO_DETECT
+        mode = black.FileMode()
+        short_mode = black.FileMode(line_length=1)
         with cache_dir() as workspace:
             path = (workspace / "file.py").resolve()
             path.touch()
-            black.write_cache({}, [path], 1, mode)
-            one = black.read_cache(1, mode)
+            black.write_cache({}, [path], mode)
+            one = black.read_cache(mode)
             self.assertIn(path, one)
-            two = black.read_cache(2, mode)
+            two = black.read_cache(short_mode)
             self.assertNotIn(path, two)
 
     def test_single_file_force_pyi(self) -> None:
-        reg_mode = black.FileMode.AUTO_DETECT
-        pyi_mode = black.FileMode.PYI
+        reg_mode = black.FileMode()
+        pyi_mode = black.FileMode(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)
-            result = CliRunner().invoke(black.main, [str(path), "--pyi"])
-            self.assertEqual(result.exit_code, 0)
+            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(black.DEFAULT_LINE_LENGTH, pyi_mode)
+            pyi_cache = black.read_cache(pyi_mode)
             self.assertIn(path, pyi_cache)
-            normal_cache = black.read_cache(black.DEFAULT_LINE_LENGTH, reg_mode)
+            normal_cache = black.read_cache(reg_mode)
             self.assertNotIn(path, normal_cache)
         self.assertEqual(actual, expected)
 
     @event_loop(close=False)
     def test_multi_file_force_pyi(self) -> None:
-        reg_mode = black.FileMode.AUTO_DETECT
-        pyi_mode = black.FileMode.PYI
+        reg_mode = black.FileMode()
+        pyi_mode = black.FileMode(is_pyi=True)
         contents, expected = read_data("force_pyi")
         with cache_dir() as workspace:
             paths = [
@@ -1063,15 +1276,14 @@ class BlackTestCase(unittest.TestCase):
             for path in paths:
                 with open(path, "w") as fh:
                     fh.write(contents)
-            result = CliRunner().invoke(black.main, [str(p) for p in paths] + ["--pyi"])
-            self.assertEqual(result.exit_code, 0)
+            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(black.DEFAULT_LINE_LENGTH, pyi_mode)
-            normal_cache = black.read_cache(black.DEFAULT_LINE_LENGTH, reg_mode)
+            pyi_cache = black.read_cache(pyi_mode)
+            normal_cache = black.read_cache(reg_mode)
             for path in paths:
                 self.assertIn(path, pyi_cache)
                 self.assertNotIn(path, normal_cache)
@@ -1086,28 +1298,27 @@ class BlackTestCase(unittest.TestCase):
         self.assertFormatEqual(actual, expected)
 
     def test_single_file_force_py36(self) -> None:
-        reg_mode = black.FileMode.AUTO_DETECT
-        py36_mode = black.FileMode.PYTHON36
+        reg_mode = black.FileMode()
+        py36_mode = black.FileMode(target_versions=black.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)
-            result = CliRunner().invoke(black.main, [str(path), "--py36"])
-            self.assertEqual(result.exit_code, 0)
+            self.invokeBlack([str(path), *PY36_ARGS])
             with open(path, "r") as fh:
                 actual = fh.read()
-            # verify cache with --py36 is separate
-            py36_cache = black.read_cache(black.DEFAULT_LINE_LENGTH, py36_mode)
+            # verify cache with --target-version is separate
+            py36_cache = black.read_cache(py36_mode)
             self.assertIn(path, py36_cache)
-            normal_cache = black.read_cache(black.DEFAULT_LINE_LENGTH, reg_mode)
+            normal_cache = black.read_cache(reg_mode)
             self.assertNotIn(path, normal_cache)
         self.assertEqual(actual, expected)
 
     @event_loop(close=False)
     def test_multi_file_force_py36(self) -> None:
-        reg_mode = black.FileMode.AUTO_DETECT
-        py36_mode = black.FileMode.PYTHON36
+        reg_mode = black.FileMode()
+        py36_mode = black.FileMode(target_versions=black.PY36_VERSIONS)
         source, expected = read_data("force_py36")
         with cache_dir() as workspace:
             paths = [
@@ -1117,17 +1328,14 @@ class BlackTestCase(unittest.TestCase):
             for path in paths:
                 with open(path, "w") as fh:
                     fh.write(source)
-            result = CliRunner().invoke(
-                black.main, [str(p) for p in paths] + ["--py36"]
-            )
-            self.assertEqual(result.exit_code, 0)
+            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 --py36 is separate
-            pyi_cache = black.read_cache(black.DEFAULT_LINE_LENGTH, py36_mode)
-            normal_cache = black.read_cache(black.DEFAULT_LINE_LENGTH, reg_mode)
+            # 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(path, pyi_cache)
                 self.assertNotIn(path, normal_cache)
@@ -1135,7 +1343,9 @@ class BlackTestCase(unittest.TestCase):
     def test_pipe_force_py36(self) -> None:
         source, expected = read_data("force_py36")
         result = CliRunner().invoke(
-            black.main, ["-", "-q", "--py36"], input=BytesIO(source.encode("utf8"))
+            black.main,
+            ["-", "-q", "--target-version=py36"],
+            input=BytesIO(source.encode("utf8")),
         )
         self.assertEqual(result.exit_code, 0)
         actual = result.output
@@ -1204,8 +1414,7 @@ class BlackTestCase(unittest.TestCase):
 
     def test_invalid_include_exclude(self) -> None:
         for option in ["--include", "--exclude"]:
-            result = CliRunner().invoke(black.main, ["-", option, "**()(!!*)"])
-            self.assertEqual(result.exit_code, 2)
+            self.invokeBlack(["-", option, "**()(!!*)"], exit_code=2)
 
     def test_preserves_line_endings(self) -> None:
         with TemporaryDirectory() as workspace:
@@ -1226,6 +1435,7 @@ class BlackTestCase(unittest.TestCase):
             result = runner.invoke(
                 black.main, ["-", "--fast"], input=BytesIO(contents.encode("utf8"))
             )
+            self.assertEqual(result.exit_code, 0)
             output = runner.stdout_bytes
             self.assertIn(nl.encode("utf8"), output)
             if nl == "\n":
@@ -1250,7 +1460,7 @@ class BlackTestCase(unittest.TestCase):
         try:
             list(black.gen_python_files_in_dir(path, root, include, exclude, report))
         except ValueError as ve:
-            self.fail("`get_python_files_in_dir()` failed: {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()
@@ -1288,6 +1498,163 @@ class BlackTestCase(unittest.TestCase):
             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)
+
+    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
+    def test_blackd_main(self) -> None:
+        with patch("blackd.web.run_app"):
+            result = CliRunner().invoke(blackd.main, [])
+            if result.exception is not None:
+                raise result.exception
+            self.assertEqual(result.exit_code, 0)
+
+
+class BlackDTestCase(AioHTTPTestCase):
+    async def get_application(self) -> web.Application:
+        return blackd.make_app()
+
+    # TODO: remove these decorators once the below is released
+    # https://github.com/aio-libs/aiohttp/pull/3727
+    @skip_if_exception("ClientOSError")
+    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
+    @unittest_run_loop
+    async def test_blackd_request_needs_formatting(self) -> None:
+        response = await self.client.post("/", data=b"print('hello world')")
+        self.assertEqual(response.status, 200)
+        self.assertEqual(response.charset, "utf8")
+        self.assertEqual(await response.read(), b'print("hello world")\n')
+
+    @skip_if_exception("ClientOSError")
+    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
+    @unittest_run_loop
+    async def test_blackd_request_no_change(self) -> None:
+        response = await self.client.post("/", data=b'print("hello world")\n')
+        self.assertEqual(response.status, 204)
+        self.assertEqual(await response.read(), b"")
+
+    @skip_if_exception("ClientOSError")
+    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
+    @unittest_run_loop
+    async def test_blackd_request_syntax_error(self) -> None:
+        response = await self.client.post("/", data=b"what even ( is")
+        self.assertEqual(response.status, 400)
+        content = await response.text()
+        self.assertTrue(
+            content.startswith("Cannot parse"),
+            msg=f"Expected error to start with 'Cannot parse', got {repr(content)}",
+        )
+
+    @skip_if_exception("ClientOSError")
+    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
+    @unittest_run_loop
+    async def test_blackd_unsupported_version(self) -> None:
+        response = await self.client.post(
+            "/", data=b"what", headers={blackd.VERSION_HEADER: "2"}
+        )
+        self.assertEqual(response.status, 501)
+
+    @skip_if_exception("ClientOSError")
+    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
+    @unittest_run_loop
+    async def test_blackd_supported_version(self) -> None:
+        response = await self.client.post(
+            "/", data=b"what", headers={blackd.VERSION_HEADER: "1"}
+        )
+        self.assertEqual(response.status, 200)
+
+    @skip_if_exception("ClientOSError")
+    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
+    @unittest_run_loop
+    async def test_blackd_invalid_python_variant(self) -> None:
+        async def check(header_value: str, expected_status: int = 400) -> None:
+            response = await self.client.post(
+                "/", data=b"what", headers={blackd.PYTHON_VARIANT_HEADER: header_value}
+            )
+            self.assertEqual(response.status, expected_status)
+
+        await check("lol")
+        await check("ruby3.5")
+        await check("pyi3.6")
+        await check("py1.5")
+        await check("2.8")
+        await check("py2.8")
+        await check("3.0")
+        await check("pypy3.0")
+        await check("jython3.4")
+
+    @skip_if_exception("ClientOSError")
+    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
+    @unittest_run_loop
+    async def test_blackd_pyi(self) -> None:
+        source, expected = read_data("stub.pyi")
+        response = await self.client.post(
+            "/", data=source, headers={blackd.PYTHON_VARIANT_HEADER: "pyi"}
+        )
+        self.assertEqual(response.status, 200)
+        self.assertEqual(await response.text(), expected)
+
+    @skip_if_exception("ClientOSError")
+    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
+    @unittest_run_loop
+    async def test_blackd_python_variant(self) -> None:
+        code = (
+            "def f(\n"
+            "    and_has_a_bunch_of,\n"
+            "    very_long_arguments_too,\n"
+            "    and_lots_of_them_as_well_lol,\n"
+            "    **and_very_long_keyword_arguments\n"
+            "):\n"
+            "    pass\n"
+        )
+
+        async def check(header_value: str, expected_status: int) -> None:
+            response = await self.client.post(
+                "/", data=code, headers={blackd.PYTHON_VARIANT_HEADER: header_value}
+            )
+            self.assertEqual(response.status, expected_status)
+
+        await check("3.6", 200)
+        await check("py3.6", 200)
+        await check("3.6,3.7", 200)
+        await check("3.6,py3.7", 200)
+
+        await check("2", 204)
+        await check("2.7", 204)
+        await check("py2.7", 204)
+        await check("3.4", 204)
+        await check("py3.4", 204)
+
+    @skip_if_exception("ClientOSError")
+    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
+    @unittest_run_loop
+    async def test_blackd_line_length(self) -> None:
+        response = await self.client.post(
+            "/", data=b'print("hello")\n', headers={blackd.LINE_LENGTH_HEADER: "7"}
+        )
+        self.assertEqual(response.status, 200)
+
+    @skip_if_exception("ClientOSError")
+    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
+    @unittest_run_loop
+    async def test_blackd_invalid_line_length(self) -> None:
+        response = await self.client.post(
+            "/", data=b'print("hello")\n', headers={blackd.LINE_LENGTH_HEADER: "NaN"}
+        )
+        self.assertEqual(response.status, 400)
+
 
 if __name__ == "__main__":
     unittest.main(module="test_black")