Is it possible to mock a return value of a function called within another function I am trying to test? I would like the mocked method (which will be called in many methods I'm testing) to returned my specified variables each time it is called. For example:
class Foo:
def method_1():
results = uses_some_other_method()
def method_n():
results = uses_some_other_method()
In the unit test, I would like to use mock to change the return value of uses_some_other_method()
so that any time it is called in Foo
, it will return what I defined in @patch.object(...)
This question is related to
python
unit-testing
mocking
patch
To add to Silfheed's answer, which was useful, I needed to patch multiple methods of the object in question. I found it more elegant to do it this way:
Given the following function to test, located in module.a_function.to_test.py
:
from some_other.module import SomeOtherClass
def add_results():
my_object = SomeOtherClass('some_contextual_parameters')
result_a = my_object.method_a()
result_b = my_object.method_b()
return result_a + result_b
To test this function (or class method, it doesn't matter), one can patch multiple methods of the class SomeOtherClass
by using patch.object()
in combination with sys.modules
:
@patch.object(sys.modules['module.a_function.to_test'], 'SomeOtherClass')
def test__should_add_results(self, mocked_other_class):
mocked_other_class().method_a.return_value = 4
mocked_other_class().method_b.return_value = 7
self.assertEqual(add_results(), 11)
This works no matter the number of methods of SomeOtherClass
you need to patch, with independent results.
Also, using the same patching method, an actual instance of SomeOtherClass
can be returned if need be:
@patch.object(sys.modules['module.a_function.to_test'], 'SomeOtherClass')
def test__should_add_results(self, mocked_other_class):
other_class_instance = SomeOtherClass('some_controlled_parameters')
mocked_other_class.return_value = other_class_instance
...
Let me clarify what you're talking about: you want to test Foo
in a testcase, which calls external method uses_some_other_method
. Instead of calling the actual method, you want to mock the return value.
class Foo:
def method_1():
results = uses_some_other_method()
def method_n():
results = uses_some_other_method()
Suppose the above code is in foo.py
and uses_some_other_method
is defined in module bar.py
. Here is the unittest:
import unittest
import mock
from foo import Foo
class TestFoo(unittest.TestCase):
def setup(self):
self.foo = Foo()
@mock.patch('foo.uses_some_other_method')
def test_method_1(self, mock_method):
mock_method.return_value = 3
self.foo.method_1(*args, **kwargs)
mock_method.assert_called_with(*args, **kwargs)
If you want to change the return value every time you passed in different arguments, mock
provides side_effect
.
This can be done with something like this:
# foo.py
class Foo:
def method_1():
results = uses_some_other_method()
# testing.py
from mock import patch
@patch('Foo.uses_some_other_method', return_value="specific_value"):
def test_some_other_method(mock_some_other_method):
foo = Foo()
the_value = foo.method_1()
assert the_value == "specific_value"
Here's a source that you can read: Patching in the wrong place
Source: Stackoverflow.com