'Test that is_usable() doesn\'t crash when the database disconnects.
Regression for #21553.'

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

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