mock could be smarter and inspect the spec's signature

[pitrou]

BPO	17015
Nosy	@pitrou, @ezio-melotti, @merwok, @voidspace
Dependencies	bpo-17071: Signature.bind() fails with a keyword argument named "self"
Files	issue17015.patch issue17015-3.patch

^{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 = <Date 2013-02-02.23:29:01.035>
created_at = <Date 2013-01-22.12:44:11.909>
labels = ['type-feature', 'library']
title = "mock could be smarter and inspect the spec's signature"
updated_at = <Date 2013-02-02.23:29:01.034>
user = 'https://github.com/pitrou'

bugs.python.org fields:

activity = <Date 2013-02-02.23:29:01.034>
actor = 'pitrou'
assignee = 'none'
closed = True
closed_date = <Date 2013-02-02.23:29:01.035>
closer = 'pitrou'
components = ['Library (Lib)']
creation = <Date 2013-01-22.12:44:11.909>
creator = 'pitrou'
dependencies = ['17071']
files = ['28886', '28903']
hgrepos = []
issue_num = 17015
keywords = ['patch']
message_count = 9.0
messages = ['180381', '180382', '180886', '180945', '180976', '180981', '180982', '181229', '181230']
nosy_count = 5.0
nosy_names = ['pitrou', 'ezio.melotti', 'eric.araujo', 'michael.foord', 'python-dev']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue17015'
versions = ['Python 3.4']

[pitrou]

This is a bit annoying:

>>> def f(a, b): pass
... 
>>> mock = Mock(spec=f)
>>> mock(1, 2)
<Mock name='mock()' id='140654219634288'>
>>> mock.assert_called_with(1, 2)
>>> mock.assert_called_with(a=1, b=2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/antoine/cpython/default/Lib/unittest/mock.py", line 726, in assert_called_with
    raise AssertionError(msg)
AssertionError: Expected call: mock(b=2, a=1)
Actual call: mock(1, 2)

This means your test assertions will depend unduly on some code style details (whether some function is called using positional or keyword arguments).
Note: if this is fixed, it should be made to work with method calls too.

[pitrou]

(note: also fails if I use mock = Mock(wraps=f) instead of mock = Mock(spec=f))

[pitrou]

Proof-of-concept patch. mock is ugly!

[pitrou]

Here is a new patch, making all assert_*_call methods work as well as autospeccing, and adding tests. Not sure I'm forgetting something else.

[voidspace]

Wow, impressive work Antoine - thanks. I am a little concerned that this relies on Python 3 only features of inspect, and *in fact* relies on bug fixes in Python 3.4 to work. That means it would be hard / impossible for the backport "mock" to have the new feature. That may be solveable (there is a backport of function signatures which mock could use for example).

[pitrou]

I am a little concerned that this relies on Python 3 only features of
inspect, and *in fact* relies on bug fixes in Python 3.4 to work.

The bug fix has landed in 3.3 as well ;-)
(see 49fd1c8aeca5)
I guess a backport of inspect.signature() would allow it to work on previous Pythons, too.

[voidspace]

Ah, well if the bugfix exists everywhere that function signatures exist then it shouldn't be a problem. (I think there is already a backport of inspect.signature() by Nick Coghlan.)

[python-dev]

New changeset b888c9043566 by Antoine Pitrou in branch 'default':
Issue bpo-17015: When it has a spec, a Mock object now inspects its signature when matching calls, so that arguments can be matched positionally or by name.
http://hg.python.org/cpython/rev/b888c9043566

[pitrou]

Committed!