mock.patch decorating a generator returns a regular function.

[shoshber]

BPO	27341
Nosy	@terryjreedy, @rbtcollins, @voidspace, @shoshber, @tirkarthi
Files	silentfail.py: example tests actual.out: output

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2016-06-17.05:35:08.841>
labels = ['type-bug', 'tests']
title = 'mock.patch decorating a generator returns a regular function.'
updated_at = <Date 2019-12-13.11:13:51.134>
user = 'https://github.com/shoshber'

bugs.python.org fields:

activity = <Date 2019-12-13.11:13:51.134>
actor = 'xtreak'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Tests']
creation = <Date 2016-06-17.05:35:08.841>
creator = 'shoshber'
dependencies = []
files = ['43443', '43444']
hgrepos = []
issue_num = 27341
keywords = []
message_count = 6.0
messages = ['268709', '268749', '268757', '268758', '268761', '268762']
nosy_count = 5.0
nosy_names = ['terry.reedy', 'rbcollins', 'michael.foord', 'shoshber', 'xtreak']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'test needed'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue27341'
versions = ['Python 3.5', 'Python 3.6']

[shoshber]

(at least in my case)

I committed two tests before I realized the tests were not being run: https://github.com/nipy/nipype/blob/abe7920a051f1570ccce4b71f26f50102d6e4e12/nipype/testing/tests/test_utils.py#L23

I realized this afternoon, while writing some more tests, that tests with the patch decorator were all reported as "OK", even when I wanted them to fail. Turns out they aren't being run at all.

I commented out all the yield statements, and the tests ran just as they should.

I don't know exactly what is going on here, but might raising an error or warning be good here?

Originally filed here: testing-cabal/mock#366

[terryjreedy]

3.2 to 3.4 only get security fixes

please provide a simple test that fails now and that you think should pass or at least warn.

[rbtcollins]

There are two related things here.

Firstly, the generator's body will run without the patch (because the wrapping function has

try:
return decorated(..)
finally:
unpwatch()

Secondly, the wrapping function is itself not a generator, and anything that introspects functions to see if they are generators will not detect the wrapped function as one - which is I suspect whats tripping nose up, but I haven't actually checked the nose code to see what its doing/expecting.

[rbtcollins]

Once fixed in CPython, we'll put the backport in mock, for folk using older Python's.

[shoshber]

I attached a file with 4 tests and the output. nosetests reports that all four tests were executed. In reality, only two tests were executed.

[shoshber]

output