python type_error ai_generated true

AssertionError: ValueError not raised During handling of the above exception, another exception occurred: TypeError: 'ValueError' object is not callable

ID: python/unittest-mock-side-effect-not-raised

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80%Fix Rate
90%Confidence
0Evidence
2024-02-28First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
3.11 active — — —
3.12 active — — —

Root Cause

mock.side_effect was set to an exception instance instead of the exception class; mock tries to call the instance and raises TypeError instead of the intended exception.

generic

中文

mock.side_effect 被设置为异常实例而不是异常类；mock 尝试调用该实例并抛出 TypeError，而非预期的异常。

Workarounds

  1. 96% success 
    from unittest import mock

with mock.patch('myapp.fetch') as m:
    m.side_effect = ValueError  # class, not ValueError()
    with pytest.raises(ValueError):
        call_sut()
  2. 94% success 
    def boom(*args, **kwargs):
    raise ValueError('bad input')

with mock.patch('myapp.fetch', side_effect=boom):
    with pytest.raises(ValueError, match='bad input'):
        call_sut()

Dead Ends

Common approaches that don't work:

  1. 90% fail

    return_value returns the exception object as the call result; it is never raised, so the test still fails.

  2. 85% fail

    Masks the mock misconfiguration and makes the test pass for the wrong reason; the SUT never actually raised.