Increase test coverage for `filecmp` by Bolotnyj · Pull Request #159663 · python/cpython

Bolotnyj · 2026-10-18T09:41:53Z

Added new unit tests to improve test coverage for the filecmp module.

Changes:

Added test_cache_overflow_and_hit to FileCompareTestCase.
Created a new isolated test class DirCmpImplementationTests to test dircmp internals through the public API (without relying on implementation details like phase2 or phase4_closure).
Added test_dircmp_os_errors_in_processing to verify OSError handling.
Added test_dircmp_different_types_and_funny_types to check type handling behavior.
Added test_dircmp_closure_and_report_funnies to verify recursive closure processing and report output.
Replaced boilerplate try/finally blocks with standard self.addCleanup() calls for reliable resource cleanups.

bedevere-app · 2026-10-18T09:42:00Z

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

picnixz · 2026-10-19T02:59:21Z

Please don't just change the issue title. Simply wait for a maintainer to add corresponding labels if necessary.

picnixz · 2026-10-19T03:00:02Z

@@ -0,0 +1 @@
+Added new unit tests to improve test coverage for the filecmp module.


There is no need for that NEWS entry.

picnixz

Don't put the tests just after the setUp() method, it doesn't make sense. Please be more mindful of existing code.
What are we exactly testing and for which reason exactly as well? phase2() looks like a private (despite its public name) method which doesn't make sense to test specifically (it's not documented in https://docs.python.org/3/library/filecmp.html).
Are we simply testing incomplete findings that only occur in phase2()? we usually don't test implementation details like that though.
A lot of your tests seem to share a common setup. Why not extending setUp() or simply create a new class just for testing phase2?

picnixz · 2026-10-19T03:00:18Z

+                if os.path.exists(d_path):
+                    os.rmdir(d_path)
+
+    def test_dircmp_invalid_attribute_error(self):


Why should we add this test? it's a useless test IMO.

picnixz · 2026-10-19T03:01:31Z

+        try:
+            with patch("os.stat", side_effect=fake_stat):
+                dc = filecmp.dircmp(self.dir, self.dir_same)
+                dc.phase2()
+                self.assertIn(trigger_file, dc.common_funny)
+        finally:
+            for d in (self.dir, self.dir_same):
+                p = os.path.join(d, trigger_file)
+                if os.path.exists(p):
+                    os.remove(p)


Use self.addCleanup and a shutil.rmtree call.

picnixz · 2026-10-19T03:01:36Z

+
+                self.assertIn(file_diff_type, dc.common_funny)
+                self.assertIn(file_funny_type, dc.common_funny)
+        finally:


bedevere-app · 2026-10-19T03:05:51Z

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

Bolotnyj · 2026-10-19T03:51:18Z

Picnixz, I have taken your words into account and will correct the errors.

Bolotnyj · 2026-10-21T10:45:41Z

I have made the requested changes; please review again.

bedevere-app · 2026-10-21T10:45:47Z

Thanks for making the requested changes!

@picnixz: please review the changes made to this pull request.

picnixz · 2026-10-21T17:16:11Z

+import stat
+import io


Pleae keep the list of imports sorted with the existing ones.

picnixz · 2026-10-21T17:17:46Z


+class DirCmpImplementationTests(unittest.TestCase):
+    def setUp(self):
+        tmpdir = tempfile.gettempdir()


For the the tempdir, I suggest that you use os_helper.temp_dir() instead.

picnixz · 2026-10-21T17:19:17Z

+        subdir_path = os.path.join(self.dir, 'subdir')
+        os.mkdir(subdir_path)
+        dir_file_path = os.path.join(self.dir, "file")
+        with open(dir_file_path, 'w', encoding="utf-8") as output:


To reduce all those checks, can you acutlaly use pathlib.Path objects so that you can directly do dir_file_path.write_text(data) or subdir_path.mkdir(parents=True, exist_ok=True) as well?

picnixz · 2026-10-21T17:24:43Z

+            _ = dc.subdirs
+            dc.phase4_closure()
+
+            with patch("sys.stdout", new=io.StringIO()) as mock_stdout:


Use support.captured_stdout() instead here.

picnixz · 2026-10-21T17:25:04Z

+                self.assertIn("Common funny cases", output)
+                self.assertIn("Trouble with common files", output)


Leave those assertions out of the context.

picnixz · 2026-10-21T17:25:10Z

+
+            with patch("sys.stdout", new=io.StringIO()) as mock_stdout:
+                dc.report()
+                output = mock_stdout.getvalue()


And this one as well

Fix PEP 8 formatting Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

picnixz · 2026-10-31T19:37:26Z

Yeah, but I don't think we really need to achieve 100%. Is there a way to test phase4 without directly invoking it? (and without some weird tests)

Bolotnyj · 2026-10-31T19:39:52Z

I will try to get this done as soon as possible.

picnixz · 2026-10-31T19:45:28Z

You don't need to rush. If it's too complex or if you can't find a simple way of testing it, I can also accept the test as is. Adding tests for common_funny is already a good contribution!

Bolotnyj · 2026-10-31T20:03:17Z

I will try to find a solution. Even if I don’t, I’ll still gain some experience. I simply want to contribute as much as I can to Python, as I genuinely love this language. @picnixz, I also want to thank you for such quick responses and high-quality reviews—you’ve been a great help!

Bolotnyj · 2026-11-01T14:26:46Z

@picnixz Yes, this was difficult for me. Please accept the tests as is.

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

picnixz · 2026-11-02T07:52:19Z

The enterContext() trick is solely for the setUp(). The other CM usages need to be with a with+block

…t, and move assertIn outside

picnixz · 2026-11-02T08:53:17Z

You have a lint error (likely because of whitespaces/tabs)

picnixz · 2026-11-02T09:32:53Z

+        Path(self.dir_diff_file, 'file2').write_text('Different contents.\n')
+
+    # Test dircmp behavior when os.stat raises OSError on specific files.
+    # Structure contains 'error_trigger_file.txt' in both directories.
+    def test_dircmp_os_errors_in_processing(self):


Suggested change

Path(self.dir_diff_file, 'file2').write_text('Different contents.\n')

# Test dircmp behavior when os.stat raises OSError on specific files.

# Structure contains 'error_trigger_file.txt' in both directories.

def test_dircmp_os_errors_in_processing(self):

Path(self.dir_diff_file, 'file2').write_text('Different contents.\n')

def tearDown(self):

filecmp.clear_cache()

# Test dircmp behavior when os.stat raises OSError on specific files.

# Structure contains 'error_trigger_file.txt' in both directories.

def test_dircmp_os_errors_in_processing(self):

picnixz · 2026-11-02T09:35:26Z

+
+            return st
+
+        with patch("os.stat", side_effect=fake_stat_types):


Usually, side_effect is used for raising exceptions. For replacing functions, I believe we can use patch(name, new_callable) or wraps= directly. I never remember exactly what's the exact form though.

picnixz · 2026-11-02T09:35:43Z

+
+        with patch("os.stat", side_effect=fake_stat_types):
+            dc = filecmp.dircmp(self.dir, self.dir_same)
+            dc.common_funny


Suggested change

dc.common_funny

No need for accessing common_funny here.

I tried moving it out, but the test fails. filecmp.dircmp uses lazy properties, so it doesn't actually call os.stat until we access dc.common_funny. We have to keep this access inside the with patch block, otherwise the mock uninstalls too early.

Registered the cache cleanup via addCleanup to keep the test environment isolated. Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

picnixz · 2026-11-02T09:47:54Z

There are a few bits I want to edit so Iwill do it myself so that it's easier. Once you're done editing on your side, I'll directly push to your branch and then we can get this merged.

picnixz · 2026-11-02T09:48:41Z

Once I pushed to your branch, don't forget to update your local fork by pulling first (so that if you want to later add more things, you can do it; but remember to never force-push)

Increase test coverage for filecmp module

6441227

bedevere-app Bot added awaiting review tests Tests in the Lib/test dir labels Oct 18, 2026

📜🤖 Added by blurb_it.

78aad17

Bolotnyj changed the title ~~[skip issue] Increase test coverage for filecmp module~~ skip issue Increase test coverage for filecmp module Oct 18, 2026

Bolotnyj changed the title ~~skip issue Increase test coverage for filecmp module~~ skip issue test_filecmp: Increase test coverage for filecmp module Oct 18, 2026

Bolotnyj changed the title ~~skip issue test_filecmp: Increase test coverage for filecmp module~~ gh-122409: Increase test coverage for filecmp module Oct 18, 2026

Bolotnyj changed the title ~~gh-122409: Increase test coverage for filecmp module~~ gh-122410: Increase test coverage for filecmp module Oct 18, 2026

Bolotnyj changed the title ~~gh-122410: Increase test coverage for filecmp module~~ skip issue test_filecmp: Increase test coverage for filecmp module Oct 18, 2026

Bolotnyj changed the title ~~skip issue test_filecmp: Increase test coverage for filecmp module~~ test_filecmp: Increase test coverage for filecmp module Oct 18, 2026

picnixz added skip issue skip news labels Oct 19, 2026

picnixz reviewed Oct 19, 2026

View reviewed changes

picnixz previously requested changes Oct 19, 2026

View reviewed changes

bedevere-app Bot removed the awaiting review label Oct 19, 2026

bedevere-app Bot added the awaiting changes label Oct 19, 2026

picnixz changed the title ~~test_filecmp: Increase test coverage for filecmp module~~ Increase test coverage for filecmp module Oct 19, 2026

picnixz changed the title ~~Increase test coverage for filecmp module~~ Increase test coverage for filecmp Oct 19, 2026

Bolotnyj added 2 commits October 19, 2026 23:06

Remove unnecessary NEWS entry

f781d4c

Refactor dircmp tests to use public API and clean up resources

0062674

bedevere-app Bot added awaiting change review and removed awaiting changes labels Oct 21, 2026

bedevere-app Bot requested a review from picnixz October 21, 2026 10:45

picnixz reviewed Oct 21, 2026

View reviewed changes

Apply suggestion from @picnixz

c68621b

Fix PEP 8 formatting Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

picnixz reviewed Nov 1, 2026

View reviewed changes

Comment thread Lib/test/test_filecmp.py Resolved

picnixz reviewed Nov 1, 2026

View reviewed changes

Comment thread Lib/test/test_filecmp.py Resolved

picnixz reviewed Nov 1, 2026

View reviewed changes

Comment thread Lib/test/test_filecmp.py Resolved

picnixz reviewed Nov 1, 2026

View reviewed changes

Comment thread Lib/test/test_filecmp.py Resolved

picnixz reviewed Nov 1, 2026

View reviewed changes

Comment thread Lib/test/test_filecmp.py Resolved

Bolotnyj and others added 3 commits November 2, 2026 12:40

Apply suggestion from @picnixz

c2e2245

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

Remove unused cm variable

54dfe05

Refactor tests

2046e40

Bolotnyj added 4 commits November 2, 2026 12:53

Refactor tests

b3825d8

Remove unused subdirs access

95b5e2a

Remove trailing whitespaces

5c9f85a

Keep with-blocks for patch CMs, trigger lazy properties inside contex…

b14bd17

…t, and move assertIn outside

Bolotnyj added 2 commits November 2, 2026 14:21

Trigger CI lint check

793cc79

Remove trailing whitespaces in test_filecmp

3c5f09f

picnixz reviewed Nov 2, 2026

View reviewed changes

Comment thread Lib/test/test_filecmp.py Resolved

picnixz reviewed Nov 2, 2026

View reviewed changes

Apply suggestion from @picnixz

3e6e54f

Registered the cache cleanup via addCleanup to keep the test environment isolated. Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

Add tearDown for cache cleanup

fffa266

		@@ -0,0 +1 @@
		Added new unit tests to improve test coverage for the filecmp module.

		self.assertIn("Common funny cases", output)
		self.assertIn("Trouble with common files", output)


		return st

		with patch("os.stat", side_effect=fake_stat_types):

		import stat
		import io

Conversation

Bolotnyj commented Oct 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

bedevere-app Bot commented Oct 18, 2026

Uh oh!

picnixz commented Oct 19, 2026

Uh oh!

Choose a reason for hiding this comment

Uh oh!

picnixz left a comment

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

bedevere-app Bot commented Oct 19, 2026

Uh oh!

Bolotnyj commented Oct 19, 2026

Uh oh!

Bolotnyj commented Oct 21, 2026

Uh oh!

bedevere-app Bot commented Oct 21, 2026

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

picnixz commented Oct 31, 2026

Uh oh!

Bolotnyj commented Oct 31, 2026

Uh oh!

picnixz commented Oct 31, 2026

Uh oh!

Bolotnyj commented Oct 31, 2026

Uh oh!

Bolotnyj commented Nov 1, 2026

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

picnixz commented Nov 2, 2026

Uh oh!

picnixz commented Nov 2, 2026

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

picnixz commented Nov 2, 2026

Uh oh!

picnixz commented Nov 2, 2026

Uh oh!

Reviewers

Uh oh!

Assignees

Labels

Projects

Milestone

Bolotnyj commented Oct 18, 2026 •

edited

Loading