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diff --git a/HACKING.rst b/HACKING.rst index cff4bcfa..ad00bf04 100644 --- a/HACKING.rst +++ b/HACKING.rst @@ -214,12 +214,67 @@ The following guidelines should be followed: * For example, ``m_readurl`` (which would be a mock for ``readurl``) +* The ``assert_*`` methods that are available on ``Mock`` and + ``MagicMock`` objects should be avoided, as typos in these method + names may not raise ``AttributeError`` (and so can cause tests to + silently pass). An important exception: if a ``Mock`` is + `autospecced`_ then misspelled assertion methods *will* raise an + ``AttributeError``, so these assertion methods may be used on + autospecced ``Mock`` objects. + + For non-autospecced ``Mock`` s, these substitutions can be used + (``m`` is assumed to be a ``Mock``): + + * ``m.assert_any_call(*args, **kwargs)`` => ``assert + mock.call(*args, **kwargs) in m.call_args_list`` + * ``m.assert_called()`` => ``assert 0 != m.call_count`` + * ``m.assert_called_once()`` => ``assert 1 == m.call_count`` + * ``m.assert_called_once_with(*args, **kwargs)`` => ``assert + [mock.call(*args, **kwargs)] == m.call_args_list`` + * ``m.assert_called_with(*args, **kwargs)`` => ``assert + mock.call(*args, **kwargs) == m.call_args_list[-1]`` + * ``m.assert_has_calls(call_list, any_order=True)`` => ``for call in + call_list: assert call in m.call_args_list`` + + * ``m.assert_has_calls(...)`` and ``m.assert_has_calls(..., + any_order=False)`` are not easily replicated in a single + statement, so their use when appropriate is acceptable. + + * ``m.assert_not_called()`` => ``assert 0 == m.call_count`` + +* Test arguments should be ordered as follows: + + * ``mock.patch`` arguments. When used as a decorator, ``mock.patch`` + partially applies its generated ``Mock`` object as the first + argument, so these arguments must go first. + * ``pytest.mark.parametrize`` arguments, in the order specified to + the ``parametrize`` decorator. These arguments are also provided + by a decorator, so it's natural that they sit next to the + ``mock.patch`` arguments. + * Fixture arguments, alphabetically. These are not provided by a + decorator, so they are last, and their order has no defined + meaning, so we default to alphabetical. + +* It follows from this ordering of test arguments (so that we retain + the property that arguments left-to-right correspond to decorators + bottom-to-top) that test decorators should be ordered as follows: + + * ``pytest.mark.parametrize`` + * ``mock.patch`` + +* When there are multiple patch calls in a test file for the module it + is testing, it may be desirable to capture the shared string prefix + for these patch calls in a module-level variable. If used, such + variables should be named ``M_PATH`` or, for datasource tests, + ``DS_PATH``. + .. _pytest: https://docs.pytest.org/ .. _pytest fixtures: https://docs.pytest.org/en/latest/fixture.html .. _TestGetPackageMirrorInfo: https://github.com/canonical/cloud-init/blob/42f69f410ab8850c02b1f53dd67c132aa8ef64f5/cloudinit/distros/tests/test_init.py\#L15 .. _TestPrependBaseCommands: https://github.com/canonical/cloud-init/blob/master/cloudinit/tests/test_subp.py#L9 .. _assertion introspection: https://docs.pytest.org/en/latest/assert.html .. _pytest 3.0: https://docs.pytest.org/en/latest/changelog.html#id1093 +.. _autospecced: https://docs.python.org/3.8/library/unittest.mock.html#autospeccing Type Annotations ---------------- |