Python unittest and mock: Check if a function gets called, but then stop the test

Question

Let's say I want to make sure that certain flags etc get dispatched properly so that deep within my library, a particular function gets called:

high_order_function_call(**kwargs) deep down contains library_function_call() and I want to make sure that it gets actually called.

The typical example given for this uses mock.patch:

@mock.patch('library')
def test_that_stuff_gets_called(self, mock_library):
    high_order_function_call(some_example_keyword='foo')
    mock_library.library_function_call.assert_called_with(42)

Now in that case, I have to wait for the entire execution of all the stuff in high_order_function_call. What if I want execution to stop and jump back to my unit test as soon as mock_library.library_function_call gets reached?

Answer 1

You could try using an exception raising side effect on the call, and then catch that exception in your test.

from mock import Mock, patch
import os.path

class CallException(Exception):
    pass

m = Mock(side_effect=CallException('Function called!'))
def caller_test():
    os.path.curdir()
    raise RuntimeError("This should not be called!")

@patch("os.path.curdir", m)
def test_called():
    try:
        os.path.curdir()
    except CallException:
        print "Called!"
        return
    assert "Exception not called!"

if __name__ == "__main__":
    test_called()