'is_usable() doesn\'t crash when the database disconnects (#21553).'

@skipUnlessDBFeature('test_db_allows_multiple_connections')
def test_is_usable_after_database_disconnects(self):

    with connection.cursor():
        pass
    connection._close()
    try:
        self.assertFalse(connection.is_usable())
    finally:
        with suppress(Exception):
            connection.close()
