def test_magnitude_of_velocity_is_given_by_pythagoras_theorem(self):
start_position = Position()
end_position = Position(4, 3)
velocity = Velocity(start_position, end_position)
self.assertEquals(5, velocity.magnitude())
def test_magnitude_is_zero_if_start_and_end_positions_are_the_same(self):
position = Position(1, 1)
velocity = Velocity(position, position)
self.assertEquals(0, velocity.magnitude())