public void unregister(String pluginId) {
        Assert.notNull(pluginId, "The pluginId must not be null.");
        if (!pluginMappingInfo.containsKey(pluginId)) {
            return;
        }
        pluginMappingInfo.remove(pluginId).forEach(this::unregisterMapping);
    }
@Test
    void unregister() {
        UserController userController = mock(UserController.class);
        // register handler methods first
        handlerMapping.registerHandlerMethods("fakePlugin", userController);
        assertThat(handlerMapping.getMappings("fakePlugin")).hasSize(1);

        // unregister
        handlerMapping.unregister("fakePlugin");
        assertThat(handlerMapping.getMappings("fakePlugin")).isEmpty();
    }