Mocker 0.10 and trivial patch-mocking of existing objects

Mocker 0.10 is out, with a number of improvements!

While we’re talking about Mocker, here is another interesting use case, exploring a pretty unique feature it offers.

Suppose we want to test that a method hello() on an object will call self.show(“Hello world!”) at some point. Let’s say that the code we want to test is this:

 class Greeting(object):

     def show(self, sentence):
         print sentence

     def hello(self):
         self.show("Hello world!")

This is the entire test method:

def test_hello(self):
    # Define expectation.
    mock = self.mocker.patch(Greeting)
    mock.show("Hello world!")
    self.mocker.replay()

    # Rock on!
    Greeting().hello()

This has helped me in practice a few times already, when testing some involved situations.

Note that you can also passthrough the call. In other words, the call may actually be made on the real method, and mocker will just assert that the call was really made, whatever the effect is.

One more important point: mocker ensures that the real method exists in the real object, and has a specification compatible with the call made. If it doesn’t, and assertion error is raised in the test with a nice error message.

UPDATE: The method for doing this is actually mocker.patch() rather than mocker.mock(), as documented. Apologies.