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@nyergler
Created September 11, 2013 23:11
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Use mock.patch to inspect calls to a method under test.
import collections
from mock import patch
MethodCall = collections.namedtuple(
'MethodCall',
('args',
'kwargs',
'return_value',
),
)
class MethodInspector(object):
"""Wrap a method and track calls to allow making assertions about them.
In some cases mocking a method isn't sufficient: we need to
inspect calls and their return values to determine that our code
is operating as expected. For example, the payment service doesn't
lend itself to mocking, but we can inspect the return value of
Order.charge_via_payment_service to assert that the right amount
was charged.
MethodInspector is a context manager that instruments a method and
tracks its arguments and return values to allow this sort of testing.
>>> with MethodInspector(Order, 'charge_via_payment_service') as inspector:
... # do something
The calls are stored as a sequence of named tuples. Each has three values:
# args
# kwargs
# return_value
"""
def __init__(self, klass, method_name):
self.klass = klass
self.method_name = method_name
self.orig = getattr(klass, method_name)
def __enter__(self):
self.calls = []
def wrapper(*a, **kw):
result = self.orig(*a, **kw)
self.calls.append(
MethodCall(
args=a,
kwargs=kw,
return_value=result,
)
)
return result
self._patch = patch.object(self.klass, self.method_name, autospec=True)
self._patch.start().side_effect = wrapper
return self
def __exit__(self, *a):
self._patch.stop()
def assertCalledOnce(self, msg=None):
if len(self.calls) != 1:
raise AssertionError(msg or '')
@stdweird
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@nyergler would it be possible to add a license header?

@nyergler
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@stdweird This code seems like an obvious use of the excellent Mock library. I don't believe it rises to the level of "creative expression" to qualify for copyright (and ergo license).

In the interest of complete clarity, I waive any copyright over this gist and dedicate to the public domain under the CC0 dedication.

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