def test_delta_should_return_2_element_tuple(self):
point = EarthPoint(x=1, y=2, altitude=5)
self.assertEqual(tuple, type(point.delta(0, 0)))
self.assertEqual(2, len(point.delta(0, 0)))
def test_delta_should_apply_negative_increase_to_y(self):
point = EarthPoint(x=1, y=2, altitude=5)
delta = point.delta(5, -3)
self.assertEqual(2 - 3, delta[1])
def test_delta_should_apply_nil_increase_to_y(self):
point = EarthPoint(x=1, y=2, altitude=5)
delta = point.delta(0, 0)
self.assertEqual(2, delta[1])
def test_delta_should_apply_negative_increase_to_x(self):
point = EarthPoint(x=1, y=2, altitude=5)
delta = point.delta(-5, 2)
self.assertEqual(1 - 5, delta[0])
