How to unit test using patch with a side effect with Pytest parametrize?

Question

I'm trying to test my function that takes in 3 arguments and also contains another function which I'm trying to mock. The issue is that the mock does not cycle through the side effect; I can't 'match' the first set of values I want to test (the first parametrized arguments) with the first value in the side effect; the second set of parametrized arguments with the second value in the side effect and so forth.

I tried to use fixtures and played around with parametrize but to no avail.

TEST CODE

# I go through each set of values I want to test with a different expected output
@pytest.mark.parametrize('banner, year, month, expected', [
    ('ctr', 2019, 1, r'A\path\file.csv'),
    ('mks', 2019, 1, r'B\path\file.csv'),
    ('sc', 2019, 1, r'C\path\file.csv'),
    ('atm', 2019, 1, r'D\path\file.csv')
])
@mock.patch('import.path.to.function.path_formatting')
def test_files(mock_directory_path_banner, banner, year, month, expected):
    # the mocked function always returns 'ctr'
    mock_directory_path_banner.side_effect = ['ctr', 'mww', 'fgl', 'fgl']
    result = get_loyalty_sales_files(banner, year, month)
    assert expected == result

In total, there are four tests. The first passes as the parameterized test uses the correct value from the mock (ctr). However the remaining tests all fail because a new mock is not called for each parameterized test. I expect that a new mock is called each time a new parameterized set of values is cycled through, but that's not the case.

Answer 1

In the file with get_loyalty_sales_files you have something like this

import path.to.function.path_formatting

Don't use this in the @patch, instead use the same path as you would import the module locally, and then append the function you want to mock:

@patch('path.to.file.with.get_loyalty_sales_files.path_formatting')

More information on how mock.patch works can be found in the mock docs.