Add --quiet

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

diff --git a/tests/test_black.py b/tests/test_black.py
index c11fca0a9019fcaf5fbfa474c1f370e476ef7f1a..d2359cb51a3ad51c219724bca6334d4153ea7d30 100644 (file)
--- a/tests/test_black.py
+++ b/tests/test_black.py
@@ -1,6 +1,9 @@
 #!/usr/bin/env python3
 from functools import partial
 #!/usr/bin/env python3
 from functools import partial

+from io import StringIO
+import os

 from pathlib import Path
 from pathlib import Path

+import sys

 from typing import Any, List, Tuple
 import unittest
 from unittest.mock import patch
 from typing import Any, List, Tuple
 import unittest
 from unittest.mock import patch


@@ -10,27 +13,29 @@ from click import unstyle
 import black
 
 ll = 88
 import black
 
 ll = 88

-ff = partial(black.format_file, line_length=ll, fast=True)
+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
 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)"

 
 
 def dump_to_stderr(*output: str) -> str:
 
 
 def dump_to_stderr(*output: str) -> str:

-    return '\n' + '\n'.join(output) + '\n'
+    return "\n" + "\n".join(output) + "\n"

 
 
 def read_data(name: str) -> Tuple[str, str]:
     """read_data('test_name') -> 'input', 'output'"""
 
 
 def read_data(name: str) -> Tuple[str, str]:
     """read_data('test_name') -> 'input', 'output'"""

-    if not name.endswith('.py'):
-        name += '.py'
+    if not name.endswith((".py", ".out", ".diff")):
+        name += ".py"

     _input: List[str] = []
     _output: List[str] = []
     _input: List[str] = []
     _output: List[str] = []

-    with open(THIS_DIR / name, 'r', encoding='utf8') as test:
+    with open(THIS_DIR / name, "r", encoding="utf8") as test:

         lines = test.readlines()
     result = _input
     for line in lines:
         lines = test.readlines()
     result = _input
     for line in lines:

-        if line.rstrip() == '# output':
+        line = line.replace(EMPTY_LINE, "")
+        if line.rstrip() == "# output":

             result = _output
             continue
 
             result = _output
             continue
 


@@ -38,23 +43,23 @@ def read_data(name: str) -> Tuple[str, str]:
     if _input and not _output:
         # If there's no output marker, treat the entire file as already pre-formatted.
         _output = _input[:]
     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'
+    return "".join(_input).strip() + "\n", "".join(_output).strip() + "\n"

 
 
 class BlackTestCase(unittest.TestCase):
     maxDiff = None
 
     def assertFormatEqual(self, expected: str, actual: str) -> None:
 
 
 class BlackTestCase(unittest.TestCase):
     maxDiff = None
 
     def assertFormatEqual(self, expected: str, actual: str) -> None:

-        if actual != expected:
+        if actual != expected and not os.environ.get("SKIP_AST_PRINT"):

             bdv: black.DebugVisitor[Any]
             bdv: black.DebugVisitor[Any]

-            black.out('Expected tree:', fg='green')
+            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))
             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')
+            black.out("Actual tree:", fg="red")

             try:
                 exp_node = black.lib2to3_parse(actual)
                 bdv = black.DebugVisitor()
             try:
                 exp_node = black.lib2to3_parse(actual)
                 bdv = black.DebugVisitor()


@@ -65,37 +70,68 @@ class BlackTestCase(unittest.TestCase):
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_self(self) -> None:
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_self(self) -> None:

-        source, expected = read_data('test_black')
+        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)
         actual = fs(source)
         self.assertFormatEqual(expected, actual)
         black.assert_equivalent(source, actual)
         black.assert_stable(source, actual, line_length=ll)

-        with self.assertRaises(black.NothingChanged):
-            ff(THIS_FILE)
+        self.assertFalse(ff(THIS_FILE))

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

-        source, expected = read_data('../black')
+        source, expected = read_data("../black")

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

-        with self.assertRaises(black.NothingChanged):
-            ff(THIS_FILE)
+        self.assertFalse(ff(THIS_DIR / ".." / "black.py"))
+
+    def test_piping(self) -> None:
+        source, expected = read_data("../black")
+        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.YES
+            )
+            sys.stdout.seek(0)
+            actual = sys.stdout.read()
+        finally:
+            sys.stdin, sys.stdout = hold_stdin, hold_stdout
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, line_length=ll)
+
+    def test_piping_diff(self) -> None:
+        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
+        actual = actual.rstrip() + "\n"  # the diff output has a trailing space
+        self.assertEqual(expected, actual)

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

-        source, expected = read_data('../setup')
+        source, expected = read_data("../setup")

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

-        with self.assertRaises(black.NothingChanged):
-            ff(THIS_FILE)
+        self.assertFalse(ff(THIS_DIR / ".." / "setup.py"))

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

-        source, expected = read_data('function')
+        source, expected = read_data("function")

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


@@ -103,15 +139,54 @@ class BlackTestCase(unittest.TestCase):
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_expression(self) -> None:
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_expression(self) -> None:

-        source, expected = read_data('expression')
+        source, expected = read_data("expression")

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

+    def test_expression_ff(self) -> None:
+        source, expected = read_data("expression")
+        tmp_file = Path(black.dump_to_file(source))
+        try:
+            self.assertTrue(ff(tmp_file, write_back=black.WriteBack.YES))
+            with open(tmp_file) as f:
+                actual = f.read()
+        finally:
+            os.unlink(tmp_file)
+        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)
+
+    def test_expression_diff(self) -> None:
+        source, _ = read_data("expression.py")
+        expected, _ = read_data("expression.diff")
+        tmp_file = Path(black.dump_to_file(source))
+        hold_stdout = sys.stdout
+        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>")
+        finally:
+            sys.stdout = hold_stdout
+            os.unlink(tmp_file)
+        actual = actual.rstrip() + "\n"  # the diff output has a trailing space
+        self.assertEqual(expected, actual)
+

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

-        source, expected = read_data('fstring')
+        source, expected = read_data("fstring")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, line_length=ll)
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_string_quotes(self) -> None:
+        source, expected = read_data("string_quotes")

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


@@ -119,7 +194,7 @@ class BlackTestCase(unittest.TestCase):
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_comments(self) -> None:
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_comments(self) -> None:

-        source, expected = read_data('comments')
+        source, expected = read_data("comments")

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


@@ -127,7 +202,23 @@ class BlackTestCase(unittest.TestCase):
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_comments2(self) -> None:
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_comments2(self) -> None:

-        source, expected = read_data('comments2')
+        source, expected = read_data("comments2")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, line_length=ll)
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_comments3(self) -> None:
+        source, expected = read_data("comments3")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, line_length=ll)
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_comments4(self) -> None:
+        source, expected = read_data("comments4")

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


@@ -135,7 +226,7 @@ class BlackTestCase(unittest.TestCase):
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_cantfit(self) -> None:
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_cantfit(self) -> None:

-        source, expected = read_data('cantfit')
+        source, expected = read_data("cantfit")

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


@@ -143,7 +234,7 @@ class BlackTestCase(unittest.TestCase):
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_import_spacing(self) -> None:
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_import_spacing(self) -> None:

-        source, expected = read_data('import_spacing')
+        source, expected = read_data("import_spacing")

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


@@ -151,7 +242,31 @@ class BlackTestCase(unittest.TestCase):
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_composition(self) -> None:
 
     @patch("black.dump_to_file", dump_to_stderr)
     def test_composition(self) -> None:

-        source, expected = read_data('composition')
+        source, expected = read_data("composition")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, line_length=ll)
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_empty_lines(self) -> None:
+        source, expected = read_data("empty_lines")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, line_length=ll)
+
+    @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)
+
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_fmtonoff(self) -> None:
+        source, expected = read_data("fmtonoff")

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


@@ -169,60 +284,69 @@ class BlackTestCase(unittest.TestCase):
             err_lines.append(msg)
 
         with patch("black.out", out), patch("black.err", err):
             err_lines.append(msg)
 
         with patch("black.out", out), patch("black.err", err):

-            report.done(Path('f1'), changed=False)
+            report.done(Path("f1"), changed=False)

             self.assertEqual(len(out_lines), 1)
             self.assertEqual(len(err_lines), 0)
             self.assertEqual(len(out_lines), 1)
             self.assertEqual(len(err_lines), 0)

-            self.assertEqual(out_lines[-1], 'f1 already well formatted, good job.')
-            self.assertEqual(unstyle(str(report)), '1 file left unchanged.')
+            self.assertEqual(out_lines[-1], "f1 already well formatted, good job.")
+            self.assertEqual(unstyle(str(report)), "1 file left unchanged.")

             self.assertEqual(report.return_code, 0)
             self.assertEqual(report.return_code, 0)

-            report.done(Path('f2'), changed=True)
+            report.done(Path("f2"), changed=True)

             self.assertEqual(len(out_lines), 2)
             self.assertEqual(len(err_lines), 0)
             self.assertEqual(len(out_lines), 2)
             self.assertEqual(len(err_lines), 0)

-            self.assertEqual(out_lines[-1], 'reformatted f2')
+            self.assertEqual(out_lines[-1], "reformatted f2")

             self.assertEqual(
             self.assertEqual(

-                unstyle(str(report)), '1 file reformatted, 1 file left unchanged.'
+                unstyle(str(report)), "1 file reformatted, 1 file left unchanged."

             )
             )

+            self.assertEqual(report.return_code, 0)
+            report.check = True

             self.assertEqual(report.return_code, 1)
             self.assertEqual(report.return_code, 1)

-            report.failed(Path('e1'), 'boom')
+            report.check = False
+            report.failed(Path("e1"), "boom")

             self.assertEqual(len(out_lines), 2)
             self.assertEqual(len(err_lines), 1)
             self.assertEqual(len(out_lines), 2)
             self.assertEqual(len(err_lines), 1)

-            self.assertEqual(err_lines[-1], 'error: cannot format e1: boom')
+            self.assertEqual(err_lines[-1], "error: cannot format e1: boom")

             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(
                 unstyle(str(report)),

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

             )
             self.assertEqual(report.return_code, 123)
             )
             self.assertEqual(report.return_code, 123)

-            report.done(Path('f3'), changed=True)
+            report.done(Path("f3"), changed=True)

             self.assertEqual(len(out_lines), 3)
             self.assertEqual(len(err_lines), 1)
             self.assertEqual(len(out_lines), 3)
             self.assertEqual(len(err_lines), 1)

-            self.assertEqual(out_lines[-1], 'reformatted f3')
+            self.assertEqual(out_lines[-1], "reformatted f3")

             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(
                 unstyle(str(report)),

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

             )
             self.assertEqual(report.return_code, 123)
             )
             self.assertEqual(report.return_code, 123)

-            report.failed(Path('e2'), 'boom')
+            report.failed(Path("e2"), "boom")

             self.assertEqual(len(out_lines), 3)
             self.assertEqual(len(err_lines), 2)
             self.assertEqual(len(out_lines), 3)
             self.assertEqual(len(err_lines), 2)

-            self.assertEqual(err_lines[-1], 'error: cannot format e2: boom')
+            self.assertEqual(err_lines[-1], "error: cannot format e2: boom")

             self.assertEqual(
                 unstyle(str(report)),
             self.assertEqual(
                 unstyle(str(report)),

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

             )
             self.assertEqual(report.return_code, 123)
             )
             self.assertEqual(report.return_code, 123)

-            report.done(Path('f4'), changed=False)
+            report.done(Path("f4"), changed=False)

             self.assertEqual(len(out_lines), 4)
             self.assertEqual(len(err_lines), 2)
             self.assertEqual(len(out_lines), 4)
             self.assertEqual(len(err_lines), 2)

-            self.assertEqual(out_lines[-1], 'f4 already well formatted, good job.')
+            self.assertEqual(out_lines[-1], "f4 already well formatted, good job.")

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

 
     def test_is_python36(self) -> None:
         node = black.lib2to3_parse("def f(*, arg): ...\n")
 
     def test_is_python36(self) -> None:
         node = black.lib2to3_parse("def f(*, arg): ...\n")


@@ -231,17 +355,86 @@ class BlackTestCase(unittest.TestCase):
         self.assertTrue(black.is_python36(node))
         node = black.lib2to3_parse("def f(*, arg): f'string'\n")
         self.assertTrue(black.is_python36(node))
         self.assertTrue(black.is_python36(node))
         node = black.lib2to3_parse("def f(*, arg): f'string'\n")
         self.assertTrue(black.is_python36(node))

-        source, expected = read_data('function')
+        source, expected = read_data("function")

         node = black.lib2to3_parse(source)
         self.assertTrue(black.is_python36(node))
         node = black.lib2to3_parse(expected)
         self.assertTrue(black.is_python36(node))
         node = black.lib2to3_parse(source)
         self.assertTrue(black.is_python36(node))
         node = black.lib2to3_parse(expected)
         self.assertTrue(black.is_python36(node))

-        source, expected = read_data('expression')
+        source, expected = read_data("expression")

         node = black.lib2to3_parse(source)
         self.assertFalse(black.is_python36(node))
         node = black.lib2to3_parse(expected)
         self.assertFalse(black.is_python36(node))
 
         node = black.lib2to3_parse(source)
         self.assertFalse(black.is_python36(node))
         node = black.lib2to3_parse(expected)
         self.assertFalse(black.is_python36(node))
 

+    def test_debug_visitor(self) -> None:
+        source, _ = read_data("debug_visitor.py")
+        expected, _ = read_data("debug_visitor.out")
+        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):
+            black.DebugVisitor.show(source)
+        actual = "\n".join(out_lines) + "\n"
+        log_name = ""
+        if expected != actual:
+            log_name = black.dump_to_file(*out_lines)
+        self.assertEqual(
+            expected,
+            actual,
+            f"AST print out is different. Actual version dumped to {log_name}",
+        )
+
+    def test_format_file_contents(self) -> None:
+        empty = ""
+        with self.assertRaises(black.NothingChanged):
+            black.format_file_contents(empty, line_length=ll, fast=False)
+        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"
+        with self.assertRaises(black.NothingChanged):
+            black.format_file_contents(same, line_length=ll, fast=False)
+        different = "l = [1,2,3]"
+        expected = same
+        actual = black.format_file_contents(different, line_length=ll, 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)
+        self.assertEqual(str(e.exception), "Cannot parse: 1:7: return if you can")
+
+    def test_endmarker(self) -> None:
+        n = black.lib2to3_parse("\n")
+        self.assertEqual(n.type, black.syms.file_input)
+        self.assertEqual(len(n.children), 1)
+        self.assertEqual(n.children[0].type, black.token.ENDMARKER)
+
+    @unittest.skipIf(os.environ.get("SKIP_AST_PRINT"), "user set SKIP_AST_PRINT")
+    def test_assertFormatEqual(self) -> None:
+        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):
+            with self.assertRaises(AssertionError):
+                self.assertFormatEqual("l = [1, 2, 3]", "l = [1, 2, 3,]")
+
+        out_str = "".join(out_lines)
+        self.assertTrue("Expected tree:" in out_str)
+        self.assertTrue("Actual tree:" in out_str)
+        self.assertEqual("".join(err_lines), "")
+

 
 

-if __name__ == '__main__':
+if __name__ == "__main__":

     unittest.main()
     unittest.main()