def test_surface_area(r):
sphere = Sphere(1)
sphere.radius = r
assert sphere.surface_area == 4 * np.pi * r**2
def test_volume(r):
sphere = Sphere(1)
sphere.radius = r
assert sphere.volume == 4 / 3 * np.pi * r**3
def test_radius_getter_setter(r):
sphere = Sphere(r)
assert sphere.radius == r
sphere.radius = r + 1
assert sphere.radius == r + 1