New submission from Matthew Suozzo <[email protected]>:
An unfortunately common pattern over large codebases of Python tests is for
spec'd Mock instances to be provided with Mock objects as their specs. This
gives the false sense that a spec constraint is being applied when, in fact,
nothing will be disallowed.
The two most frequently observed occurrences of this anti-pattern are as
follows:
* Re-patching an existing autospec.
def setUp(self):
mock.patch.object(mod, 'Klass', autospec=True).start()
self.addCleanup(mock.patch.stopall)
@mock.patch.object(mod, 'Klass', autospec=True) # :(
def testFoo(self, mock_klass):
# mod.Klass has no effective spec.
* Deriving an autospec Mock from an already-mocked object
def setUp(self):
mock.patch.object(mod, 'Klass').start()
...
mock_klass = mock.create_autospec(mod.Klass) # :(
# mock_klass has no effective spec
This is fairly easy to detect using _is_instance_mock at patch time however it
can break existing tests.
I have a patch ready and it seems like this error case is not frequent enough
that it would be disruptive to address.
Another option would be add it as a warning for a version e.g. 3.10 and then
potentially make it a breaking change in 3.11. However considering this is a
test-only change with a fairly clear path to fix it, that might be overly
cautious.
----------
components: Tests
messages: 388532
nosy: msuozzo
priority: normal
severity: normal
status: open
title: Disallow Mock spec arguments from being Mocks
type: enhancement
versions: Python 3.10
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Python tracker <[email protected]>
<https://bugs.python.org/issue43478>
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