def METHOD_NAME(self):
    target_tokens = [
        ["Hello", "world", "!", "", "", ""],
        ["<unk>", "name", "is", "<unk>", ".", ""],
    ]
    source_tokens = [
        ["Bonjour", "le", "monde", "!", ""],
        ["Mon", "nom", "est", "Max", "."],
    ]
    attention = [
        [
            [0.9, 0.1, 0.0, 0.0, 0.0],
            [0.2, 0.1, 0.7, 0.0, 0.0],
            [0.0, 0.1, 0.1, 0.8, 0.0],
            [0.0, 0.0, 0.0, 0.0, 0.0],
            [0.0, 0.0, 0.0, 0.0, 0.0],
            [0.0, 0.0, 0.0, 0.0, 0.0],
        ],
        [
            [0.8, 0.1, 0.1, 0.0, 0.0],
            [0.1, 0.9, 0.0, 0.0, 0.0],
            [0.0, 0.1, 0.8, 0.1, 0.0],
            [0.1, 0.1, 0.2, 0.6, 0.0],
            [0.0, 0.1, 0.1, 0.3, 0.5],
            [0.0, 0.0, 0.0, 0.0, 0.0],
        ],
    ]
    replaced_target_tokens = sequence_to_sequence.replace_unknown_target(
        target_tokens, source_tokens, attention, unknown_token="<unk>"
    )
    replaced_target_tokens = self.evaluate(replaced_target_tokens)
    self.assertNotIn(b"<unk>", replaced_target_tokens.flatten().tolist())
    self.assertListEqual(
        [b"Hello", b"world", b"!", b"", b"", b""],
        replaced_target_tokens[0].tolist(),
    )
    self.assertListEqual(
        [b"Mon", b"name", b"is", b"Max", b".", b""],
        replaced_target_tokens[1].tolist(),
    )