Fix misspecified tests using MagicMock().called_with() #1072

Prior implementation ran `assert ...MagicMock.called_with(...)` `called_with` is not a real test method on MagicMock, so it returns a MagicMock instance by default, which is truthy and evaluates to true by assert. This test wasn't checking for anything and would pass no matter what actually happened in the code. These new tests check for the intended methods being called.