How to test if another class method is called within a method in python?

Question

I have the following structure:

ClassB():
   def foo():

Class A():
   def __init__(self, B):
       #some initialisations
   def method1():
       #complex logic
       B.foo()

I am trying to write a unit test method1 and would like to test if foo is called once or not. How I can achieve this? What should I mock?

Answer 1

You should create a Mock for B, pass it to the constructor of A and check if the function was called once.

You can write the Mock by yourself. E.g.:

class B_Mock():
    def __init__(self):
       self.foo_calls = 0

    def foo(self):
        self.foo_calls += 1

And than check the attr foo_calls of your B_Mock instance with assert