def remove_known_traits(trait_names):
    """ Remove the irrelevant trait names from a list of trait names in order to
    get to the useful trait names.

    Also, sort the list for ease of use in testing.
    """
    return sorted([
        x for x in trait_names
        if x not in ('_context', '_synched', 'trait_added', 'trait_modified')
    ])