test: add unit tests for parents_below() utility function

[DaanDeMeyer]

No description provided.

[behrmann]

I think the result is a bit superfluous and makes it easier to read, since it's a repeated line that doesn't do anything

Suggested change

	result = parents_below(path, below)
	assert result == [Path("/a/b/c/d"), Path("/a/b/c")]
	assert parents_below(path, below) == [Path("/a/b/c/d"), Path("/a/b/c")]

The tests that raise break this pattern.

[behrmann]

This check should be further up, since it's basically the same as _basic and doesn't really fit the pattern after the raising tests.