How to mock a method inside another method with Python unittest?

Question

I am struggling to mock a method inside another method i.e Let's say I have 2 classes A, B as follows:

class A:
 def method_A(self):
 return "Hi"
class B:
 def method_B(self):
 instance_A = A()
 result = instance_A.method_A()
 print(result)

Here I want to mock method_A while testing method_B but can't find a way. Thanks in advance

• Akalanka Weerasooriya: Are you trying to test method_B by mocking mothod_A?
• unitSphere: Yes, I want to test method_B by mocking method_A.

Answer 1

I hope this is what you are looking for.

class A:
 def method_A(self):
 return "Hi"
class B:
 def method_B(self):
 instance_A = A()
 result = instance_A.method_A()
 return result
import mock
def mock_A(self):
 return 'Bye'
def test_method_B():
 with mock.patch.object(A, 'method_A', new=mock_A):
 result = B().method_B()
 assert result == 'Bye'

Answer 2

What exactly do you mean by mocking a method? If you mean why your code isn't doing anything that's because you need to call the method afterwards:-

B.method_B()

Maybe that helps somehow, if not could you explain the problem a lil'bit more.

Answer 3

Well in that case first you wanna import mock library by simply typing import mock

then you wanna create a function for 1) Mocking

def mocking_method_A(self):
return Some_value

2)Testing

def testing_method_B():
 with mock.patch.object(A, 'method_A', new=mocking_A):
 result = B().method_B()
 assert result == Some_value