My Apex code:
public with sharing class RouteOutlet_v3{

public Integer totalCount {get;set;}
public Integer rowIndex {get;set;}
public Integer selectedDay { get; set; }
public Integer Weeklyoff{ get; set; }
public list<String> strLocation{get;set;}
public Route_Outlet__c del;
public list<Route_Outlet__c> listRouteOutlet { get; set; }
Route_Outlet__c rou= new Route_Outlet__c();  
public Route__c route{get;set;}
public list<OutletWrapper> outletWrapperList{get;set;}
public RouteOutlet_v3(ApexPages.StandardController controller) {
        route=new Route__c ();
        strLocation=new list<String>();
        outletWrapperList=new list<OutletWrapper>();
        addRouteoutlet();
}
     
public PageReference saveoutlet1(){
    if(route!=null){
       try{ 
             system.debug('&&&&&&&   '+route);
            upsert route;
            List<Route_Outlet__c> listRouteOutlet=new list<Route_Outlet__c>();
                      
            if(outletWrapperList.size()>0){
                 for(OutletWrapper olwIterator: outletWrapperList){
                   if(olwIterator.routeOutlet!=null){
                       if(olwIterator.routeOutlet.Account__c!=null){
                         Route_Outlet__c routeiterator=olwIterator.routeOutlet;
                         routeiterator.Area__c=olwIterator.outletArea;
                         routeiterator.Contact_Person__c=olwIterator.contactPerson;
                         routeiterator.Country__c=olwIterator.outletCountry;
                          routeiterator.City__c=olwIterator.outletCity;
                         routeiterator.Date__c=date.today();
                         routeiterator.Mobile_Number__c=olwIterator.outletPhone;
                         routeiterator.Pin_Code__c=olwIterator.outletPinCode;
                         routeiterator.Route__c=route.id;
                         routeiterator.State__c=olwIterator.outletState;
                         listRouteOutlet.add(routeiterator);
                       }
                   }
                 
                 }
                }
                if(listRouteOutlet.size()>0){
                         
                        system.debug('+_+_+_+_+   '+listRouteOutlet);
                        insert listRouteOutlet;
                         ApexPages.Message myMsg = new ApexPages.Message(ApexPages.Severity.Confirm,'Record Saved Successfull');
                         ApexPages.addMessage(myMsg);
                 }
                 
            }
            catch (Exception ex){
               // ApexPages.Message myMsg = new ApexPages.Message(ApexPages.Severity.Error,'Error Occurred : '+ex);
              //  ApexPages.addMessage(myMsg);
            }
        }
    else{
        ApexPages.Message myMsg = new ApexPages.Message(ApexPages.Severity.Error,'No appropriate Route found.');
        ApexPages.addMessage(myMsg);
    }
    
    return null;
} 
public void ClearAll(){
    if(listRouteOutlet!=null)
        listRouteOutlet.clear();
        route.Name='';
        route.Date__c=null;
        route.City__c=null;
        selectedDay=null;
        Weeklyoff=null;                       
        outletWrapperList.clear();
        ApexPages.getMessages().clear();
        route=new Route__c ();
  
}
public void fetchMapLocation(){
       strLocation=new list<String>();
       if(outletWrapperList.size()>0){
           for(OutletWrapper olwIterator: outletWrapperList){
           if(olwIterator.routeOutlet!=null){
               if(olwIterator.routeOutlet.Account__c!=null){
                     //strLocation.add(olwIterator.outletArea);
                  strLocation.add(olwIterator.outletCity);
               }
           }
         }
       }
}
public void addPopulatedAccounttoRouteOutlet(){
        rowIndex = Integer.valueOf(ApexPages.currentPage().getParameters().get('rowIndex'));
        OutletWrapper olwWrap=outletWrapperList.get(rowIndex);
        Account acc=[Select id,BillingStreet,BillingCity,BillingState,BillingCountry,BillingPostalCode,Phone from Account where Id=: olwWrap.routeOutlet.Account__c];
        olwWrap.outletArea=acc.BillingStreet;
         olwWrap.outletCity=acc.BillingCity;
        olwWrap.outletState=acc.BillingState;
        olwWrap.outletCountry=acc.BillingCountry;
        olwWrap.outletPinCode=acc.BillingPostalCode;
        olwWrap.outletPhone=acc.Phone;
        fetchMapLocation();
}
public void addRouteoutlet(){
    Route_Outlet__c rOutlet=new Route_Outlet__c ();
    OutletWrapper olw=new OutletWrapper();
    olw.routeOutlet=rOutlet;
    outletWrapperList.add(olw);
}

public void deleteRouteoutlet(){
    rowIndex = Integer.valueOf(ApexPages.currentPage().getParameters().get('rowIndex'));
    outletWrapperList.remove(rowIndex);
    fetchMapLocation();
}

public class OutletWrapper{
 public Route_Outlet__c routeOutlet{get;set;}
 public string outletArea{get;set;}
 public string contactPerson{get;set;}
 public string outletCountry{get;set;}
 public string outletCity{get;set;}
 public string outletState{get;set;}
 public string outletPinCode{get;set;}
 public string outletPhone{get;set;}
 public OutletWrapper(){}
 public OutletWrapper(Route_Outlet__c routeOutlet,string outletArea,string contactPerson,string outletCountry,string outletCity,string outletState,string outletPinCode,string outletPhone){
   this.routeOutlet=routeOutlet;
   this.outletArea=outletArea;
   this.outletCity=outletCity;
   this.contactPerson=contactPerson;
   this.outletCountry=outletCountry;
   this.outletState=outletState;
   this.outletPinCode=outletPinCode;
   this.outletPhone=outletPhone;
 }
}         
}
My Test class:
@isTest
private class TestRouteOutlet_v3 {
    static testMethod void runTestRoutes() {
        Account a = new Account(
            Name = 'Test Account ',
            BillingStreet = 'Test Street ',
            BillingCity = 'Test City ',
            BillingCountry = 'Test Country '
        );
        insert a;

        City__c c = new City__c(Name = 'Test City ' );
        insert  c;

        Route__c rou = new Route__c(
            Name = 'Test route ',
            Date__c = System.today(),
            City__c =c.Id
        );
        insert rou;

        Route_Outlet__c routeOutlet = new Route_Outlet__c(
            Account__c = a.Id,
            Route__c = rou.Id
        );
        insert routeOutlet ;

        Integer index = 0;

        PageReference reference = Page.RouteOutlet_v3;
        reference.getParameters().put('rowIndex', String.valueOf(index));
        Test.setCurrentPage(reference);

        ApexPages.StandardController sc = new ApexPages.StandardController(rou);
        RouteOutlet_v3 rotout = new RouteOutlet_v3(sc);

        rotout.addRouteoutlet();
        rotout.addPopulatedAccounttoRouteOutlet();
        rotout.deleteRouteoutlet();
        rotout.saveoutlet1();
    }
}

I am geting  Error, in this Function/line:
public void addPopulatedAccounttoRouteOutlet(){
        rowIndex = Integer.valueOf(ApexPages.currentPage().getParameters().get('rowIndex'));
        OutletWrapper olwWrap=outletWrapperList.get(rowIndex);
        Account acc=[Select id,BillingStreet,BillingCity,BillingState,BillingCountry,BillingPostalCode,Phone from Account where Id=: olwWrap.routeOutlet.Account__c];
        olwWrap.outletArea=acc.BillingStreet;
         olwWrap.outletCity=acc.BillingCity;
        olwWrap.outletState=acc.BillingState;
        olwWrap.outletCountry=acc.BillingCountry;
        olwWrap.outletPinCode=acc.BillingPostalCode;
        olwWrap.outletPhone=acc.Phone;
        fetchMapLocation();
}
The Error is:
System.QueryException: List has no rows for assignment to SObject
Class.RouteOutlet_v3.addPopulatedAccounttoRouteOutlet: