def test_string():
assert anagrams.of("") == ""
def test_four_letters():
assert len(anagrams.of("ABCD")) == 24
def test_two_letters():
assert anagrams.of("AB") == ["AB", "BA"]
def test_three_letters():
assert anagrams.of("ABC") == ["ABC", "ACB", "BAC", "BCA", "CAB", "CBA"]
def test_one_letter():
assert anagrams.of("A") == "A"