Python Mock - How to get the return of a MagicMock as if it was a normal method

Question

For example:

import mock

class MyClass(object):
    def foo(self, x, y, z):
        return (x, y, z)


class TestMyClass(TestCase)
    @mock.patch('MyClass')
    def TestMyClass(self, MyClassMock):
        foo_mock = MyClassMock.foo()

        self.assertEquals((x, y, z), foo_mock)

So, the real question is: How to get the return of that test intead of getting this <MagicMock name='MyClass.foo()' id='191728464'> or how to deal with this MagicMock object to get the return of that test which should be a tuple containing 3 elements and nothing more or less?

Any suggestion, any idea, any argument will be welcome. Thanks in advance!

Solution

If you trying to test if MyClass.foo() works correctly, you should not mock it.

Mocking is used for anything outside the code-under-test; if foo called another, external function some_module.bar(), then you'd mock some_module.bar() and give it a staged return value:

import some_module

class MyClass(object):
    def foo(self, x, y, z):
        result = some_module.bar(x, y, z)
        return result[0] + 2, result[1] * 2, result[2] - 2

class TestMyClass(TestCase):
    @mock.patch('some_module.bar')
    def test_myclass(self, mocked_bar):
        mocked_bar.return_value = (10, 20, 30)

        mc = MyClass()

        # calling MyClass.foo returns a result based on bar()
        self.assertEquals(mc.foo('spam', 'ham', 'eggs'),
            (12, 40, 28))
        # some_class.bar() was called with the original arguments
        mocked_bar.assert_called_with('spam', 'ham', 'eggs')

Here I set mocked_bar.return_value to what should be returned when the mocked some_module.bar() function is called. When the code-under-test actually calls bar(), the mock returns that value.

When you don't set a return_value a new MagicMock() object is returned instead, one that'll support further calls, and you can test for those calls just like on the mocked_bar object, etc.