def test_inits_heads(elements: List[int]) -> None:
"""inits(elements)[:1] == [[], [elements[0]]."""
assert sut.inits(elements)[0] == []
assert sut.inits(elements)[1] == [elements[0]]
def test_inits_monotonic_length(elements: List[int]) -> None:
"""[len(x) for xs in inits(elements)] == range(len(elements) + 1)."""
lengths = [len(xs) for xs in sut.inits(elements)]
assert lengths == list(range(len(elements) + 1))
def test_inits_length(elements: List[int]) -> None:
"""len(inits(elements)) == len(elements) + 1."""
assert len(sut.inits(elements)) == len(elements) + 1