Doubling objects in unittest.mock

Question

I am trying to use unittest with unittest.mock to do some tests in my application.

I have two classes MainClass and Caller. I would like to test main class with a double Caller. This is in short what I have:

class MainClass:

 def __init__(self, caller):
   self.caller = caller

 def some_function(self):
   self.caller.function1()
   blab = self.caller.function2()

class Caller:

 # some functions non of which should be accessed in tests


class CallerMock:
  def __init__(self):
   self.items = []

  def function1(self):
   pass

  def function2(self):
    return items

In the test I do:

class TestMainFunction(unittest.TestCase):

    def setUp(self):
        self.mock = MagicMock(wraps=CallerMock())
        self.main_class = MainClass(self.mock)

    def test(self):
        # self.main_class.caller.items = items
        # self.mock.items = items
        # self.mock.function2.return_value = items
        self.main_class.some_functions()
        # non of the above change the return value of function2

However the problem is that non of the commented lines actually change the return value of my function2. How can I achieve this?

I would be also happy with a solution where I don't need the double and all the functions of the Caller would return None and I would have to specify the return values of functions in particular tests.

Answer 1

You could just mock the Caller , and patch the call() method. That way, you won't need a double:

def setUp(self):
    self.mocked_caller = mock.Mock(spec=Caller)
    self.mocked_caller.call.return_value = items
    self.main_class = MainClass(self.mocked_caller)

def test(self):
    self.main_class.some_function()
    self.assertTrue(self.mocked_caller.called)