public static AbstractProtocolNegotiatorBuilderSingleton getSingleton() {
        return SINGLETON;
    }
@Test
    void testSingletonInstance() {
        AbstractProtocolNegotiatorBuilderSingleton singleton1 = ClusterProtocolNegotiatorBuilderSingleton.getSingleton();
        AbstractProtocolNegotiatorBuilderSingleton singleton2 = ClusterProtocolNegotiatorBuilderSingleton.getSingleton();
        assertSame(singleton1, singleton2);
    }