def test_generate_prefixes(self):
a, b, sep = 'a', 'b', os.sep
assert list(Nested._generate_prefixes(sep)) == []
assert list(Nested._generate_prefixes('')) == []
assert list(Nested._generate_prefixes('.')) == []
a_sep_b = a + sep + b
assert list(Nested._generate_prefixes(a_sep_b)) == [a_sep_b, a]
sep_a_sep_b = sep + a + sep + b
assert list(Nested._generate_prefixes(sep_a_sep_b)) == [sep_a_sep_b, sep + a]
