Hi Gurus,
have writtern the apex aura enabled controller for controller and also the test class,please help me in fixing and writing detailed test class for below upsert apex class

apex controller

public class PickListHandler {
   @AuraEnabled
   public static List<LavelWrapper> getLevel1(string recID){
       List<String> tempLst1 = new List<String>();
       list<LavelWrapper> lstWrap=new list<LavelWrapper>();
       //  System.debug('recid'+recID);
       list<ERT_Case_Type__c>  lstertcase=new list<ERT_Case_Type__c>();
       lstertcase=[select id,Level_1__c,Level_2__c,Level_3__c from ERT_Case_Type__c where id=:recID];//fetch data based on it
       string strL1,strL2,strL3;
       if(lstertcase.size()>0){
           strL1=lstertcase[0].Level_1__c;
           strL2=lstertcase[0].Level_2__c;
           strL3=lstertcase[0].Level_3__c;
       }
       //  System.debug(strL2+'recid'+strL1);
       for(AggregateResult  ar : [select Level_1__c,COUNT(id) from Case_Type_Data__c  group by Level_1__c]) {
           LavelWrapper obj= new LavelWrapper();
           string strLav1=(string)ar.get('Level_1__c');
           obj.strLavelType='recL1';
           obj.strL1val=strLav1;
           if(strLav1==strL1)
               obj.isSelected=true;
           else
               obj.isSelected=false; 
           lstWrap.add(obj);
           //tempLst1.add(strLav1);
       }
       //get l2 data
       for(string ar:getLevel2(strL1)){
           if(strL1!=null){
               LavelWrapper obj= new LavelWrapper();
               // string strLav2=(string)ar.get('Level_2__c');
               string strLav2=(string)ar;
               obj.strLavelType='recL2';
               obj.strL2val=strLav2;
               if(strLav2==strL2)
                   obj.isSelected=true;
               else
                   obj.isSelected=false; 
               lstWrap.add(obj);
           }
       }
       //get l2 data
       for(string ar:getLevel3(strL1,strL2)){
           if(strL2!=null){
               LavelWrapper obj= new LavelWrapper();
               // string strLav2=(string)ar.get('Level_2__c');
               string strLav2=(string)ar;
               obj.strLavelType='recL3';
               obj.strL3val=strLav2;
               if(strLav2==strL3)
                   obj.isSelected=true;
               else
                   obj.isSelected=false; 
               lstWrap.add(obj);
           }
       }
       System.debug(' wrapper '+lstWrap);
       return lstWrap;
       
       
   } 
   
   @AuraEnabled
   public static List<String> getLevel2(string strName){
       List<String> tempLst2 = new List<String>();
       for(AggregateResult  ar : [select Level_2__c,COUNT(id) from Case_Type_Data__c where Level_1__c=:strName  group by Level_2__c])
       {
           tempLst2.add(''+ar.get('Level_2__c'));
       }
       
       return tempLst2;
       
   } 
   
   @AuraEnabled
   public static List<String> getLevel3(string strName1,string strName2){
       List<String> tempLst3 = new List<String>();
       for(AggregateResult  ar : [select Level_3__c,COUNT(id) from Case_Type_Data__c  where Level_1__c=:strName1 and Level_2__c=:strName2 group by Level_3__c])
       {
           tempLst3.add(''+ar.get('Level_3__c'));
       }
       
       return tempLst3;
       
       
   } 
   
   @AuraEnabled
   public  static String  savecasetype(string level1,string level2,string level3,string id){
       string strMsg='successfull';
       try{
           ERT_Case_Type__c obj=new ERT_Case_Type__c();
           
           System.debug('CASE  = '+ Obj.Case__c); 
           Obj.Level_1__c=level1;
           System.debug('Level1  = '+ Obj.Level_1__c); 
           Obj.Level_2__c=level2;
           System.debug('Level2  = '+ Obj.Level_2__c); 
           Obj.Level_3__c=level3;
           System.debug('Level3  = '+ Obj.Level_3__c);
           if(id.startsWithIgnoreCase('500'))
               Obj.Case__c = id;
           else
               obj.id=id;
           upsert  obj;
           
       }
       
       catch(Exception ex){
           strMsg='error';
       }
       return strMsg;  
   }
   
   public class LavelWrapper{
       @AuraEnabled
       public string strLavelType{get;set;}
       @AuraEnabled
       public string strL1val{get;set;}
       @AuraEnabled
       public string strL2val{get;set;}
       @AuraEnabled
       public string strL3val{get;set;}
       @AuraEnabled
       public boolean isSelected{get;set;}
       
   }
   
   
   
}

Here is test class

@IsTest
public class testGetAllLevels { 

@IsTest
static  void testGetLevel1()
{
    Case_Type_Data__c obj = new Case_Type_Data__c();
    obj.Level_1__c = 'Test Level 1';
    insert obj;
    List<String> s = PickListHandler.getLevel1();

}

@IsTest
static void testGetLevel2()
{
    Case_Type_Data__c obj = new Case_Type_Data__c();
    obj.Level_1__c = 'Test Level 1';
    insert obj;
    List<String> s = PickListHandler.getLevel2('Test Level 1');

}
    
@IsTest
static void testGetLevel3()
{
    Case_Type_Data__c obj = new Case_Type_Data__c();
    obj.Level_1__c = 'Test Level 1';
    obj.Level_2__c = 'Test Level 2';
    obj.Level_3__c = 'Test Level 3';
    insert obj;
    List<String> s = PickListHandler.getLevel3('Test Level 1','Test Level 2');

}
    
@IsTest 
static  void testsaveCaseType(){
        // Create the Case Record.
        Case cas = new Case(Status ='New', Priority = 'Medium', Origin = 'Email'); 
        insert cas;
       
        ERT_Case_Type__c obj=new ERT_Case_Type__c();
        string one='one';
        string two='two';
        string three='three';
        test.startTest();
        String testing=PickListHandler.savecasetype(one,two,three,cas.id);
        test.stopTest();
    }
    

    
 
    
}

Here is error while running test class

== Test Summary
NAME                 VALUE                                
───────────────────  ─────────────────────────────────────
Outcome              Failed                               
Tests Ran            1                                    
Pass Rate            0%                                   
Fail Rate            100%                                 
Skip Rate            0%                                   
Test Run Id          7072F00001g7Xqs                      
Test Execution Time  null ms     

=== Test Results
TEST NAME                   OUTCOME      MESSAGE                                                                                                           RUNTIME (MS)
──────────────────────────  ───────────  ────────────────────────────────────────────────────────────────────────────────────────────────────────────────  ────────────
testGetAllLevels.<compile>  CompileFail  line 10, column 38: Method does not exist or incorrect signature: void getLevel1() from the type PickListHandler  null

Your help is needed and appreciated

Fiona