@Test
public void merge() {

    ClickListenerRegistry registry2 = new ClickListenerRegistry();
    registry2.registerListener("registry2", (a, b) -> {
    }, true);
    registry2.registerListener("registry3", (a, b) -> {
    }, true);
    registry.registerListener("registry", (a, b) -> {
    }, true);
    registry.merge(registry2);
    assertTrue(registry.getRegisteredListeners().containsKey("registry"));
    assertTrue(registry.getRegisteredListeners().containsKey("registry2"));
    assertTrue(registry.getRegisteredListeners().containsKey("registry3"));
}