How do i setup a unittest method that checks a method inside method?

Hello guys! I have been practicing my code testing skills with unittest, and one of the holes I found in my knowlage is how to test a method, that calles other method inside of it, that requires attributes. For example:

def calc_balance(usr_input)
    new_balance = total_income() - usr_input
    return new_balance

def total_income(value):
    return value

I want to test with unittest, for example: if usr_input = 100, and my total_income() method returns 50, the test will pass if new_balance will be equal to 50.

I know how to write a test for calc_balance() that assigns usr_inputs value (that's easy), but i don't know how to pass a value to total_income().

I'll be glad if someone could help me with that... i couldn't any usful info... I assume that maybe I need to use the seUp() method or something like that...