Return list of names of currently signed in users.

    :param session: SQLAlchemy session through which to access the database.
    :param today: (optional) The current date as a `datetime.date` object. Used for testing.
    :param full_name: (optional) Whether to display full user names, or just first names.
    :return: List of currently signed in users.

def signed_in_users(session=None, today=None, full_name=True):
    """Return list of names of currently signed in users.

    :param session: SQLAlchemy session through which to access the database.
    :param today: (optional) The current date as a `datetime.date` object. Used for testing.
    :param full_name: (optional) Whether to display full user names, or just first names.
    :return: List of currently signed in users.
    """ # noqa
    if session is None:
        session = Session()
    else:
        session = session

    if today is None:
        today = date.today()
    else:
        today = today

    signed_in_users = (
        session
        .query(User)
        .filter(Entry.date == today)
        .filter(Entry.time_out.is_(None))
        .filter(User.user_id == Entry.user_id)
        .all()
    )

    session.close()
    return signed_in_users