CODEWITHSUNDEEP
pythonpytest
Yes
Yes

Reputation: 433

pytest: creating a mock object for a function with a different return value depending on the input

I want to test a function that makes use of the builtins.open function and want to return a value depending on which path was provided. So far my function looks like this:

@pytest.fixture
def mock_open(self,mocker):
    mock_file = mocker.patch('builtins.open', return_value=StringIO("mock open"))
    return mock_file

Is there a way to say "if path==a then return "mock a", else return "mock b"?

Upvotes: 0

Views: 1789

Answers (1)

Niel Godfrey P. Ponciano
Niel Godfrey P. Ponciano

Reputation: 10719

Use side_effect to intercept the call to open() and act accordingly based on the file parameter.

@pytest.fixture
def mock_open(self, mocker):
    def _mock_open(file, *args, **kwargs):
        if file == "a":
            return StringIO("For a")
        return StringIO("For b")
    mock_file = mocker.patch('builtins.open', side_effect=_mock_open)
    return mock_file

Upvotes: 2

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