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!

Answer 1

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.