[TIP] I don't get it?

WW teetee at gmail.com
Tue Nov 2 09:43:24 PDT 2010

On Tue, Nov 2, 2010 at 12:17 PM, Michael Foord <fuzzyman at voidspace.org.uk>wrote:

>  On 02/11/2010 15:34, WW wrote:
> Hello,
> This is my first time using the python mock library and I'm a little
> confused.  I'd like to provide some guarantees that my mocks are being
> called with the correct number of arguments.  The documentation seems to
> indicate there are two ways to do this, "spec" and "mocksignature", but it's
> a little unclear to me what the difference is supposed to be between them.
> I find myself using the @patch.object decorator almost all the time,
> because the modules I'm testing use a lot of top-level functions from
> modules they've imported.  When I do something like this:
> @patch.object(somemodule, 'somemethod', spec=True)
> You should still be able to use patch with a named function (as a string).
> See the other replies for an example.

Does this work if I'm trying to patch a global variable rather than a
function in another module?

It doesn't seem to have any effect; I can call somemodule.somemethod with
> any combination of invalid arguments and no exceptions are thrown.
> Using spec doesn't protect you against being called with invalid arguments.
> You should get an error when you validate that the calls were made correctly
> when you call 'assert_called_with'.
assert_called_with is fine if I know the exact values I want the function to
be called with, but I'm just trying to make sure that a function was called
with the correct number of arguments.  If spec can't do this, then what is
spec supposed to be used for?  I'm still unclear as to what the difference
is between spec and mocksignature and why both exist.

> However, when I do:
> @patch.object(somemodule, 'somemethod', mocksignature=True)
> I get:
> Traceback (most recent call last):
>   File "/usr/lib/python2.6/site-
> packages/mock-0.7.0b3-py2.6.egg/mock.py", line 485, in patched
>     arg = patching.__enter__()
>   File "/usr/lib/python2.6/site-packages/mock-0.7.0b3-py2.6.egg/mock.py",
> line 536, in __enter__
>     new_attr = mocksignature(original, new)
>   File "/usr/lib/python2.6/site-packages/mock-0.7.0b3-py2.6.egg/mock.py",
> line 140, in mocksignature
>     signature, func = _getsignature(func, skipfirst)
>   File "/usr/lib/python2.6/site-packages/mock-0.7.0b3-py2.6.egg/mock.py",
> line 87, in _getsignature
>     func = func.__call__
> AttributeError: 'SentinelObject' object has no attribute '__call__'
> This is weird. The traceback implies that you are trying to replace a
> sentinel object using mocksignature (and sentinels don't have signatures to
> mock). Either that or it is a bug. I'll create a simple test case here (but
> this functionality *is* tested), but it looks like something is not quite
> setup how you expect.

Here's a small test case that produces the error in Python 2.6, CentOS 5.5:

   1. from mock import patch
   3. class tc(object):
   4.     def meth(a, b, c):
   5.         pass
   7. g = tc()
   9. @patch.object(g, 'meth', mocksignature=True)
   10. def test_g(patched):
   11.     g.meth(1)
   13. test_g()

> All the best,
> Michael Foord


> What am I missing here?
> Thanks for your help.
> _______________________________________________
> testing-in-python mailing list
> testing-in-python at lists.idyll.orghttp://lists.idyll.org/listinfo/testing-in-python
> -- http://www.voidspace.org.uk/
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