def test_angle_of_velocity_is_determined_by_the_arctangent(self):
start_position = Position()
end_posotion = Position(3, 4)
velocity = Velocity(start_position, end_posotion)
self.assertTrue(velocity.angle() > 45)
self.assertTrue(velocity.angle() < 90)
def test_angle_of_velocity_is_45_if_x_and_y_of_end_position_are_the_same(
self):
start_position = Position()
end_position = Position(2, 2)
velocity = Velocity(start_position, end_position)
self.assertEquals(45, velocity.angle())