@Override
    public String toString() {
        return "ConfigChangedEvent{" + "key='"
                + key + '\'' + ", group='"
                + group + '\'' + ", content='"
                + content + '\'' + ", changeType="
                + changeType + "} "
                + super.toString();
    }
@Test
    void testToString() {
        ConfigChangedEvent event = new ConfigChangedEvent(KEY, GROUP, CONTENT);
        assertNotNull(event.toString());
    }