gh-71339: Add additional assertion methods for unittest #128707

serhiy-storchaka · 2025-01-10T13:10:15Z

Add the following methods:

assertHasAttr() and assertNotHasAttr()
assertIsSubclass() and assertNotIsSubclass()
assertStartsWith() and assertNotStartsWith()
assertEndsWith() and assertNotEndsWith()

Also improve error messages for assertIsInstance() and assertNotIsInstance().

Issue: Additional assert methods for unittest #71339

📚 Documentation preview 📚: https://cpython-previews--128707.org.readthedocs.build/

Add the following methods: * assertHasAttr() and assertNotHasAttr() * assertIsSubclass() and assertNotIsSubclass() * assertStartswith() and assertNotStartswith() * assertEndswith() and assertNotEndswith() Also improve error messages for assertIsInstance() and assertNotIsInstance().

hugovk · 2025-01-10T13:31:16Z

Great!

assertStartsWith() and assertEndsWith() has been renamed to assertStartswith() and assertEndswith().

I recommend assertStartsWith() and assertEndsWith(), both for readability, and for accessibility -- screen readers will have a better chance with the extra capitals.

It doesn't really matter that startswith is all lower case, because we're creating a new method name.

(And we already have assertIsInstance, which checks isinstance, and not assertIsinstance.)

serhiy-storchaka · 2025-01-10T13:53:57Z

I wrote them initially as assertStartsWith() and assertEndsWith(), but renamed to assertStartswith() and assertEndswith() as the result of the discussion on the issue.

serhiy-storchaka · 2025-01-10T14:06:39Z

I created a poll: https://discuss.python.org/t/assertstartwith-vs-assertstartwith/76701.

JelleZijlstra

Looks good but I agree with Hugo that the name should be assertStartsWith.

cjw296 · 2025-01-11T18:20:56Z

Looks like the poll is pretty unanimous :-)

The changes look great, but I'll admit I'm unlikely to use them as I tend to avoid the UnitTest base class where possible now.

Doc/library/unittest.rst

Doc/whatsnew/3.14.rst

Co-authored-by: Hugo van Kemenade <[email protected]>

vstinner

LGTM. Just a few minor coding style remarks.

vstinner · 2025-01-13T07:55:17Z

Lib/unittest/case.py

@@ -1321,15 +1321,77 @@ def assertIsInstance(self, obj, cls, msg=None):
        """Same as self.assertTrue(isinstance(obj, cls)), with a nicer
        default message."""
        if not isinstance(obj, cls):
-            standardMsg = '%s is not an instance of %r' % (safe_repr(obj), cls)
+            if isinstance(cls, tuple):
+                standardMsg = '%s is not an instance of any of %r' % (safe_repr(obj), cls)


You may use f-strings :-)

Actually, '%s is not an instance of any of %r' % (safe_repr(obj), cls) and f'{safe_repr(obj)!s} is not an instance of any of {cls!r}' produce the same bytecode. So the difference is only in readability, which is at large part subjective. I was not sure that inlining expressions in f-strings would make the code more readable, but if you think so...

vstinner · 2025-01-13T07:55:41Z

Lib/unittest/case.py

            standardMsg = '%s is an instance of %r' % (safe_repr(obj), cls)
            self.fail(self._formatMessage(msg, standardMsg))

+    def assertIsSubclass(self, cls, superclass, msg=None):
+        try:
+            r = issubclass(cls, superclass)


You may avoid variables of a single letter: use "res" or "result". Same remark for new functions below.

picnixz

Just some docs nits and LGTM. I'm very happy to have assertHasAttr because I needed it a lot in my personal projects.

Doc/library/unittest.rst

vstinner · 2025-01-14T08:04:13Z

Nice additions, thanks @serhiy-storchaka.

…honGH-128707) Add a mix-in class ExtraAssertions containing the following methods: * assertHasAttr() and assertNotHasAttr() * assertIsSubclass() and assertNotIsSubclass() * assertStartsWith() and assertNotStartsWith() * assertEndsWith() and assertNotEndsWith() (cherry picked from commit 06cad77)

bedevere-app · 2025-01-14T08:53:32Z

GH-128815 is a backport of this pull request to the 3.13 branch.

…honGH-128707) Add a mix-in class ExtraAssertions containing the following methods: * assertHasAttr() and assertNotHasAttr() * assertIsSubclass() and assertNotIsSubclass() * assertStartsWith() and assertNotStartsWith() * assertEndsWith() and assertNotEndsWith() (cherry picked from commit 06cad77)

…-128707) (GH-128815) Add a mix-in class ExtraAssertions containing the following methods: * assertHasAttr() and assertNotHasAttr() * assertIsSubclass() and assertNotIsSubclass() * assertStartsWith() and assertNotStartsWith() * assertEndsWith() and assertNotEndsWith() (cherry picked from commit 06cad77)

…t.support (pythonGH-128707) (pythonGH-128815) Add a mix-in class ExtraAssertions containing the following methods: * assertHasAttr() and assertNotHasAttr() * assertIsSubclass() and assertNotIsSubclass() * assertStartsWith() and assertNotStartsWith() * assertEndsWith() and assertNotEndsWith() (cherry picked from commit c6a566e) Co-authored-by: Serhiy Storchaka <[email protected]> (cherry picked from commit 06cad77)

…-128707) (GH-128815) (GH-129059) Add a mix-in class ExtraAssertions containing the following methods: * assertHasAttr() and assertNotHasAttr() * assertIsSubclass() and assertNotIsSubclass() * assertStartsWith() and assertNotStartsWith() * assertEndsWith() and assertNotEndsWith() (cherry picked from commit c6a566e) Co-authored-by: Serhiy Storchaka <[email protected]> (cherry picked from commit 06cad77)

serhiy-storchaka requested review from JelleZijlstra, AlexWaygood, cjw296, jaraco, warsaw, FFY00 and vsajip as code owners January 10, 2025 13:10

bedevere-app bot mentioned this pull request Jan 10, 2025

Additional assert methods for unittest #71339

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bedevere-app bot added the awaiting core review label Jan 10, 2025

Fix references: "with" instead of "With".

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JelleZijlstra reviewed Jan 11, 2025

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Spell "With" instead of "with".

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cjw296 removed their request for review January 11, 2025 18:21

hugovk reviewed Jan 11, 2025

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jaraco approved these changes Jan 11, 2025

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Co-authored-by: Hugo van Kemenade <[email protected]>

vstinner approved these changes Jan 13, 2025

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Remove variable r.

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hugovk approved these changes Jan 13, 2025

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Use f-strings.

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picnixz approved these changes Jan 13, 2025

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Double empty lines.

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serhiy-storchaka merged commit 06cad77 into python:main Jan 14, 2025
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serhiy-storchaka deleted the extra-assertions branch January 14, 2025 08:02

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gh-71339: Add additional assertion methods for unittest #128707

gh-71339: Add additional assertion methods for unittest #128707

serhiy-storchaka commented Jan 10, 2025 •

edited by hugovk

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gh-71339: Add additional assertion methods for unittest #128707

gh-71339: Add additional assertion methods for unittest #128707

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serhiy-storchaka commented Jan 10, 2025 •

edited by hugovk

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