public ConnectApi.TopicPage feedItemPage{get;set;}

public CommunityGroupPage()
 {
   // Chatter Group Id
   Id groupid = apexpages.currentpage().getparameters().get('id');

   / pull all chatter groups, faster than individual queries + 1 SOQL
   chatterGroups = [SELECT id, Name, NetworkId FROM CollaborationGroup where id =: groupid Limit 1];
   String comid;
   String grpid;
   if(chatterGroups.Size() > 0)
   {
   comid = chatterGroups[0].NetworkId;
   grpid = chatterGroups[0].Id;   
   }
   
   //This will be used to fetch Recently Talking about topics for current chatter group
   feedItemPage = ConnectApi.Topics.getRecentlyTalkingAboutTopicsForGroup(comId,grpid);
   
 }

**
 * An apex page controller that exposes the Chatter Group Page functionality
 */
@IsTest global with sharing class CommunityGroupPageTest {
    @IsTest(SeeAllData=true) global static void testCommunityGroupPage () {
        // Instantiate a new controller with all parameters in the page

   Network community;
   String communityId;

   Id currentUserId = UserInfo.getUserId();    
        User usr = [select id,Name from User where id =: currentUserId];
        
        System.runAs(usr) {
        community = [SELECT id, Name,OptionsReputationEnabled FROM Network where name =: 'Customer Community'];
        communityId = community.id;
        
        collaborationgroup cg = new collaborationgroup(name ='ChatterGroupPage',CollaborationType='Public',OwnerId=currentUserId,NetworkId=communityId);
        insert cg;
        
       PageReference pageRef = Page.CommunityChatterPage;
        Test.setCurrentPage(pageRef);//Applying page context here
        // Add parameters to page URL
        ApexPages.currentPage().getParameters().put('id', cg.id);//Observe how helpful it was to set the parameters in your page from Unit test 
        
        CommunityGroupPage controller = new  CommunityGroupPage ();
        
        controller.groupid = System.currentPagereference().getParameters().get('id');

        ConnectApi.TopicPage testPage = new ConnectApi.TopicPage();
        List<ConnectApi.Topic> testItemList = new List<ConnectApi.Topic>();
        testItemList.add(new ConnectApi.Topic());
        testItemList.add(new ConnectApi.Topic());
                
        testPage.topics = testItemList;

        ConnectApi.Topics.setTestGetRecentlyTalkingAboutTopicsForGroup(communityId, cg.id, testPage);
        ConnectApi.Topics.getRecentlyTalkingAboutTopicsForGroup(communityId,cg.id); 

        }
}
}