Public with sharing  class SampleDuplicateCustomerPO_Check
{
    public void DuplicateCustomerPO_Check_method(case newcaseList)
    {
        Schema.DescribeSObjectResult d = Schema.SObjectType.Case; 
        Map<String,Schema.RecordTypeInfo> rtMapByName = d.getRecordTypeInfosByName();
        Schema.RecordTypeInfo rtByName =  rtMapByName.get('CIR');
        Id LegalRecId = rtByName.getRecordTypeId();   
        
        Case c = newcaseList;
        List<Case> CaseList2 = new List<Case>();
        List<List<case>> CaseListRam = new List<List<case>>();
        Boolean DupeFoundAllow = false; 
        
        String rtId = Schema.SObjectType.Case.getRecordTypeInfosByName().get('MCS - CS').getRecordTypeId();
        String Casenum = '';
        if(c.GE_ES_PO__c != '' && c.GE_ES_PO__c != null &&c.RecordTypeId == rtId ){    
            CaseListRam = [Find :c.GE_ES_PO__c Returning Case(CaseNumber where GE_ES_PO__c = :c.GE_ES_PO__c AND id != :c.id)];
            DupeFoundAllow = c.GE_MCS_Duplicate_PO_ok__c;
        } 
        for(List<case> cas : CaseListRam){
            CaseList2.addall(cas);
        }
        for(case ca : CaseList2){
            if(Casenum == '')
            Casenum = ca.CaseNumber;
            else
            Casenum = Casenum+','+ca.CaseNumber;
        }
        if(CaseList2.size() > 0){
            if(DupeFoundAllow){
                List<Case> CaseList3 = new List<Case>();
                
            }else{
                c.addError('There is already a Case with same Customer PO# and the CaseNumbers are: '+CaseNum+'. Please check "Duplicate PO OK?" if this is not a duplicate order!');        
            }
        }
    
    }
............................
This is my class.I am trying to write a test class for this. I tried so many ways but still i am getting 75% code coverage. For deployment this coverage is not a problem. But as per my organization I need to increase to 85%.
Please help me on this. I am posting my test class as well.
​

......................
@isTest
public class Test_Sample123{
/* usefull code commented
static testMethod void ParentCaseAutoUnfollow123()
    {
    Account acc=new Account();
    acc.name='test';
    insert acc;
    String rt= Schema.SObjectType.Case.getRecordTypeInfosByName().get('MCS - CS').getRecordTypeId();           
    Case cs=new Case();
        cs.GE_ES_PO__c='123456';
        cs.GE_MCS_Duplicate_PO_ok__c=true;
        cs.recordTypeid = rt;  
        cs.status='closed'; 
        insert cs;
        Case cs6=new Case();
        cs6.GE_ES_PO__c='123456';
        cs6.GE_MCS_Duplicate_PO_ok__c=true;
        cs6.recordTypeid = rt;  
        cs6.status='new';
        insert cs6;              
        List<case>csl=new List<case>();     
        csl.add(cs);
        csl.add(cs6);
        Map <id,case>oldMap = new Map<id,case>();
        oldmap.put(cs.id, cs);
        Map<Id,Case>oldMapCase1=(Map<Id,Case>)oldMap;
        oldMapCase1.put(cs.id, cs6);       
        cs.status='closed';
        update cs;       
        GE_OG_trg_Case_ParentCaseAutoUnfollow  cw1=new GE_OG_trg_Case_ParentCaseAutoUnfollow();
        cw1.mcsTaskUpdate(csl,oldMapCase1);        
        list<task>tslit=new List<task>();
        task t=new task();
        t.Status='In Progress';
        t.subject='test';
        t.whatid=cs.id;
        tslit.add(t);
        insert tslit;   
        GEESUtil.caseRecTypes=null;      
        GE_OG_trg_Case_ParentCaseAutoUnfollow  cw=new GE_OG_trg_Case_ParentCaseAutoUnfollow();
        cw.mcsTaskInsert(csl);        
    }      
    */      
    static testMethod void duplicatePO()
    {
    Account acc=new Account();
    acc.name='test';
    insert acc;
    
        String rt= Schema.SObjectType.Case.getRecordTypeInfosByName().get('MCS - CS').getRecordTypeId();        
        //opportunity opp=[select name from opportunity where recordtype.name='MCS' limit 1];
        List<Case> CaseList = new List<Case>();
        Case cs=new Case();
        cs.GE_ES_PO__c='123456';
        cs.GE_MCS_Duplicate_PO_ok__c=false;
        cs.recordTypeid = rt;  
        cs.status='new'; 
        caselist.add(cs);        
        //insert cs;
        cs.GE_ES_PO__c='';
        Case cs1=new Case();
        cs1.GE_ES_PO__c='1234567';
        cs1.GE_MCS_Duplicate_PO_ok__c=true;
        cs1.recordTypeid = rt;  
        cs1.status='new';
        caselist.add(cs1); 
        insert caselist;
        cs.GE_ES_PO__c='1234567';
         try
        {
            update cs;
        }
        catch(DMLException e)
        {
            
            //System.Assert(e.getMessage().contains('Recommendation should be Compliance Accepted to generate DOA'));
            System.Assert(e.getMessage().contains('There is already a Case with same Customer PO# and the CaseNumbers are'));
            
        }       
        
        /*
        List<case>caselist23=new List<case>();
        for(case cas : caselist){
            caselist23.add(cas);
        }
            caselist23.add(cs6);     
            */      
            SampleDuplicateCustomerPO_Check dup=new SampleDuplicateCustomerPO_Check();           
            String casenum='';
            //dup.DuplicateCustomerPO_Check_method(cs1);
            dup.DuplicateCustomerPO_Check_method(cs);             
    }   
    }