Create a calculator which only likes positive even numbers

[olliesilvester]

Create a calculator which accepts two user inputs:

• If either of the user inputs are negative, or odd, raise a customised Exception
• If the total is negative or odd, raise a customised Exception
• Otherwise, return the total of the two user inputs
• Handle error in an appropriate way if the user enters non-digits into the calculator

Write unit tests for all scenarios you can think of

Also manage this using a git branch

use MagicMock to test the user input (ask me about this when you get to it)