def test_polar_to_cartesian(): """Test helper transform function from polar to cartesian""" r = 1 theta = np.pi # expected values are (-1, 0) x = r * np.cos(theta) y = r * np.sin(theta) coord = _polar_to_cartesian(theta, r) # np.pi is an approx since pi is irrational assert_almost_equal(coord, (x, y), 10) assert_almost_equal(coord, (-1, 0), 10)