In typical unit tests, almost all of the dependencies are mocked or
patched (mock.patch), without any guarantee that the mocked methods
actually exist, or if their signatures are respected (see below). Because
of this, actual issues can easily be overlooked and missed, as the unit
tests are wrongfully passing.
The mock.Mock class accepts a spec as an argument, which only solves half
the problem: it only checks if an attribute exists, based on the given
spec. It does not guarantee that the given attribute is actually a method,
or if its signature is respected. Some unit tests may pass the autospec
argument, but mock doesn't support it at the moment.
mock.patch, mock.patch.object, mock.patch.multiple accept an autospec
argument, but because of a bug, it cannot be used properly.
Adds a fixture which replaces mock.Mock and mock.MagicMock with
subclass which accepts the autospec argument, and on call, it will
check the signature of the called method / function.
Adds a function which replaces mock.mock._patch with a subclass, which
treats the autospec argument properly (consumes the self / cls argument),
and sets autospec=True by default, unless otherwise specified.
WARNING: this function is not a fixture, and in order to benefit from it,
it will have to be called as EARLY as possible, before any test classes
are loaded, otherwise the original mock.mock._patch is used instead.
Needed-By: I3636833962c905faa0f144c7fdc4833037324d31
Needed-By: I4484e63c97bd1cdde3d88855eabe7545784f365e
Closes-Bug: #1735588
Change-Id: I0e4a55fbf4c1d175726ca22b664e240849a99856
0bde35899a