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unittest loaders should avoid loading test cases that are abstract base classes #120665

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unittest loaders should avoid loading test cases that are abstract base classes#120665
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testsTests in the Lib/test dirtype-bugAn unexpected behavior, bug, or error

Description

@blhsing
blhsing
opened on Jun 18, 2024

Bug report

Bug description:

As reported in Discourse, loading a TestCase-derived subclass that is also an abstract base class like the following:

import unittest
from abc import ABC, abstractmethod

class FooBase(unittest.TestCase, ABC):
    @abstractmethod
    def test(self): ...

class Foo(FooBase):
    def test(self): pass

unittest.main()

would currently result in:

TypeError: Can't instantiate abstract class FooBase without an implementation for abstract method 'test'

We should make the unittest loaders avoid loading such test cases and methods from them.

CPython versions tested on:

3.12, CPython main branch

Operating systems tested on:

Linux, Windows

Linked PRs

Activity

  1. blhsing
    added
    type-bugAn unexpected behavior, bug, or error
    on Jun 18, 2024
  2. blhsing
    added 3 commits that reference this issue on Jun 18, 2024

    pythongh-120665: make unittest loaders avoid loading test cases that …

    f0475c9

    pythongh-120665: split the test for loadTestsFromNames into two sub-t…

    55a4994

    pythongh-120665: use self.assertRaisesRegex instead of a try block

    d74e37c
  3. erlend-aasland
    added
    testsTests in the Lib/test dir
    on Jun 18, 2024

  4. serhiy-storchaka commented on Jun 18, 2024

    @serhiy-storchaka
    serhiy-storchaka
    on Jun 18, 2024
    Member

    See also previous discussion in #58739.

  5. serhiy-storchaka
    added this to Unittest & doctest issueson Jun 4, 2025
  6. github-project-automation
    moved this to Todo in Unittest & doctest issueson Jun 4, 2025

  7. JonathonReinhart commented on Jun 15, 2026

    @JonathonReinhart
    JonathonReinhart
    on Jun 15, 2026
    Contributor

    Until this issue is resolved, I hope this little snippet helps someone:

    import inspect
import unittest

# ...

class MyTestLoader(unittest.TestLoader):
    def loadTestsFromTestCase(self, testCaseClass):
        if inspect.isabstract(testCaseClass):
            return self.suiteClass()
        return super().loadTestsFromTestCase(testCaseClass)


if __name__ == "__main__":
    unittest.main(verbosity=2, testLoader=MyTestLoader())
  8. nedbat
    added a commit that references this issue on Jun 17, 2026

    gh-120665: make unittest loaders avoid loading test cases that are ab…

    5ad3c6d
  9. merwok
    marked Add means to mark unittest.TestCases as "do not load". #58739 as a duplicate of this issue on Jun 17, 2026
  10. nedbat
    added 3 commits that reference this issue on Jun 17, 2026

    [3.14] gh-120665: make unittest loaders avoid loading test cases that…

    7202313

    [3.15] gh-120665: make unittest loaders avoid loading test cases that…

    6d29a08

    [3.13] gh-120665: make unittest loaders avoid loading test cases that…

    2ca9dae
  11. philthompson10
    added a commit that references this issue on Jun 17, 2026

    pythongh-120665: make unittest loaders avoid loading test cases that …

    79d6078
  12. nedbat
    closed this as completedon Jun 18, 2026
  13. github-project-automation
    moved this from Todo to Done in Unittest & doctest issueson Jun 18, 2026
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