For unit testing, I want to mock a variable inside a function, such as:
def function_to_test(self):
foo = get_complex_data_structure() # Do not test this
do_work(foo) # Test this
I my unit test, I don't want to be dependent on what get_complex_data_structure() would return, and therefore want to set the value of foo manually.
How do I accomplish this? Is this the place for @patch.object?
Just use @patch() to mock out get_complex_data_structure():
@patch('module_under_test.get_complex_data_structure')
def test_function_to_test(self, mocked_function):
foo_mock = mocked_function.return_value
When the test function then calls get_complex_data_structure() a mock object is returned and stored in the local name foo; the very same object that mocked_function.return_value references in the above test; you can use that value to test if do_work() got passed the right object, for example.
Mock.side_effect, either to an iterable (and Python will use the next value from that iterable for each call), or a function; a function is given the same arguments so you can return a value based on those.` single backticks work. You don't need to show me how you managed to get it to work, here are other answers I gave on mocking that use .side_effect that you could reference. If you have a new question, you could create a new post on that.Assuming that get_complex_data_structure is a function1, you can just patch it using any of the various mock.patch utilities:
with mock.patch.object(the_module, 'get_complex_data_structure', return_value=something)
val = function_to_test()
...
they can be used as decorators or context managers or explicitly started and stopped using the start and stop methods.2
1If it's not a function, you can always factor that code out into a simple utility function which returns the complex data-structure
2There are a million ways to use mocks -- It pays to read the docs to figure out all the ways that you can set the return value, etc.
