def METHOD_NAME(self, encodings):
    single, pair = encodings
    assert single.token_to_chars(0) == None
    assert single.token_to_chars(2) == (2, 6)
    assert pair.token_to_chars(2) == (2, 6)
    assert pair.token_to_chars(5) == None
    assert pair.token_to_chars(6) == (0, 2)