def test_the_hit__when_some_intersections_have_negative_t():
# Given
s = Sphere()
i1 = Intersection(-1, s)
i2 = Intersection(1, s)
xs = Intersections(i2, i1)
# When
i = xs.hit()
# Then
assert i == i2
def test_the_hit__when_all_intersections_have_netative_t():
# Given
s = Sphere()
i1 = Intersection(-2, s)
i2 = Intersection(-1, s)
xs = Intersections(i2, i1)
# When
i = xs.hit()
# Then
assert i is None
def test_the_hit__when_all_intersections_have_positive_t():
# Given
s = Sphere()
i1 = Intersection(1, s)
i2 = Intersection(2, s)
xs = Intersections(i2, i1)
# When
i = xs.hit()
# Then
assert i == i1
def test_the_hit_is_always_the_lowest_nonnegative_intersection():
# Given
s = Sphere()
i1 = Intersection(5, s)
i2 = Intersection(7, s)
i3 = Intersection(-3, s)
i4 = Intersection(2, s)
xs = Intersections(i1, i2, i3, i4)
# When
i = xs.hit()
# Then
assert i == i4