Hi,

  Anyone please update the below apex class as testclass
  I have tried so many ways but no luck

 this is myapex class


public class CaseUserHelper {

    public static void updateCaseStage(List<Case> cases) {
    
             List<ID> cIds = new List<ID>();
        
             List<Case_User__c> cuser = New  List<Case_User__c>();
             Map<ID, Case_User__c> cusermap = new Map<ID, Case_User__c>();

             Set<String> skillSet = new Set<String>();
             List<String> skillSetList = new List<String>();
    
             for(Case c: cases){
        
                   if(c.Status == 'New') {
                   cIds.add(c.Id); //add case ids.
                   }     
                   skillSet.add(c.CaseRelatedTo__c);
             }   
           skillSetList.addAll(skillSet);    
        
         //available users               
           try{
                   List<Case_User__c> availableCaseUsers = [SELECT AvailableUsers__c, Timings__c, SkillSet__c  FROM Case_User__c where Availability__c = TRUE ORDER BY Last_Case_Allocated_Time__c ASC];
                 //List<Case_User__c> availableCaseUsers = Database.query(queryString);
                    integer i=0;
                    integer nomatchingSkillset = availableCaseUsers.size();
                    for(Case c: cases){
                        for(; i<=availableCaseUsers.size();i++){
                        if(availableCaseUsers.get(i).SkillSet__c.contains(c.CaseRelatedTo__c)){
                          c.OwnerId = availableCaseUsers.get(i).AvailableUsers__c;
                          availableCaseUsers.get(i).Last_Case_Allocated_Time__c = DateTime.now();
                          cusermap.put(availableCaseUsers.get(i).id, availableCaseUsers.get(i));
                         } else {
                              nomatchingSkillset--;
                              if(nomatchingSkillset == 0){
                                  //TODO assign to case queue
                                  
                                     User u =[SELECT Email FROM User WHERE Id IN (SELECT UserOrGroupId FROM GroupMember WHERE Group.DeveloperName ='CaseQueue')];
                                     String us = u.Email;
                                                          
                                      Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
                                      String[] toAddresses = new String[] {us};
                                      mail.setToAddresses(toAddresses );
                                      mail.setSubject('No Users available to handle this case');
                                      mail.plainTextBody='handle this case';
                                      Messaging.SendEmail(new Messaging.SingleEmailMessage[] {mail});
                                                          
                                  break;
                              }
                              continue;
                        }
                        if(i>=availableCaseUsers.size()){
                            i=0;
                        }
                        break;
                     }      
                }
            }catch(System.DmlException e){
            
                 System.debug('Missing the required field in record');
                 
            }catch(Exception e){
            
                 System.debug('An Error Occured at:' +e.getMessage());
                 
            }finally{
            
                 System.debug('This is block just for closing the class');
            }      
          
 
     if(!cusermap.isEmpty()) {
      update cusermap.values();
     }

        
   }
}

Thanks In Advance