    def test_derive_short_output(self, backend):
        hkdf = HKDF(
            hashes.SHA256(),
            4,
            salt=None,
            info=None,
            backend=backend
        )

        assert hkdf.derive(b"\x01" * 16) == b"gJ\xfb{"
The product receives input or data, but it does
        not validate or incorrectly validates that the input has the
        properties that are required to process the data safely and
        correctly.