def validate_mapping(_, __, values):
    """
    >>> validate_mapping(None, None, [('episode', 'TV Show'), ('movie', 'Movie')])
    [('episode', 'TV Show'), ('movie', 'Movie')]
    >>> validate_mapping(None, None, [('wrong', 'TV Show'), ('movie', 'Movie')])  # doctest: +ELLIPSIS
    Traceback (most recent call last):
    ...
    ValueError: mappings must be any of ... and not 'wrong'
    """
    valid_mappings = {"episode", "movie"}
    for (key, value) in values:
        if key not in valid_mappings:
            raise ValueError(
                f"mappings must be any of {valid_mappings} and not {key!r}"
            )

    return values