[issue36871] Misleading error from unittest.mock's assert_has_calls

[Samuel Freilich]

Samuel Freilich <sfreilich at google.com> added the comment:

This is still not totally fixed. This solves the underlying error with method specs, but not the bug that was causing the error-swallowing in assert_has_calls:

https://github.com/python/cpython/blob/ee536b2020b1f0baad1286dbd4345e13870324af/Lib/unittest/mock.py#L2216

expected = [self._call_matcher(c) for c in calls]
cause = expected if isinstance(expected, Exception) else None

isinstance(expected, Exception) is never true, because expected is always a list. It should instead be:

cause = next((e for e in expected if isinstance(e, Exception)), None)

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nosy: +sfreilich

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<https://bugs.python.org/issue36871>
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