Python Mock does not detect changed signature

test.py

from unittest.mock import Mock
import unittest.mock
import doctest

class Calculator:

    """
    >>> mock_display = Mock(Display)
    >>> calculator = Calculator(mock_display)
    >>> calculator.add(3)
    >>> calculator.add(2)
    >>> mock_display.show.assert_has_calls([
    ...     unittest.mock.call("Total = 3"),
    ...     unittest.mock.call("Total = 5"),
    ... ])
    """

    def __init__(self, display):
        self.display = display
        self.total = 0

    def add(self, amount):
        self.total += amount
        self.display.show(f"Total = {self.total}")

class Display:

    def show(self, text, color):
        """
        >>> Display().show("hello", "red")
        hello
        """
        print(text)

if __name__ == "__main__":
    doctest.testmod()
    print("OK")
    calculator = Calculator(Display())
    calculator.add(5)

$ python test.py 
OK
Traceback (most recent call last):
  File "/tmp/test.py", line 39, in <module>
    calculator.add(5)
  File "/tmp/test.py", line 24, in add
    self.display.show(f"Total = {self.total}")
TypeError: show() missing 1 required positional argument: 'color'