bpo-35330: Don't call the wrapped object if `side_effect` is set (GH10973)

* tests: Further validate `wraps` functionality in `unittest.mock.Mock`

Add more tests to validate how `wraps` interacts with other features of
mocks.

* Don't call the wrapped object if `side_effect` is set

When a object is wrapped using `Mock(wraps=...)`, if an user sets a
`side_effect` in one of their methods, return the value of `side_effect`
and don't call the original object.

* Refactor what to be called on `mock_call`

When a `Mock` is called, it should return looking up in the following
order: `side_effect`, `return_value`, `wraps`. If any of the first two
return `mock.DEFAULT`, lookup in the next option.

It makes no sense to check for `wraps` returning default, as it is
supposed to be the original implementation and there is nothing to
fallback to.

1 files changed, 4 insertions, 0 deletions

diff --git a/Misc/NEWS.d/next/Library/2018-12-06-00-43-13.bpo-35330.abB4BN.rst b/Misc/NEWS.d/next/Library/2018-12-06-00-43-13.bpo-35330.abB4BN.rst
new file mode 100644
index 0000000..24d0ab8
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-12-06-00-43-13.bpo-35330.abB4BN.rst
@@ -0,0 +1,4 @@
+When a :class:`Mock` instance was used to wrap an object, if `side_effect`
+is used in one of the mocks of it methods, don't call the original
+implementation and return the result of using the side effect the same way
+that it is done with return_value.