query==select id, stageName,AccountId, Account.Rating from opportunity where stageName IN ('workInprogress,Delivered,Closed won') AND AccountId !=Null

global class UpdateAccountRating implements Database.Batchable<sObject>, Database.Stateful {
    global Integer recordsProcessed = 0;
 global  Database.QueryLocator start(Database.BatchableContext bc) {
     set<string> strlist = new set<string>{'workInprogress','Delivered','ClosedWon'};
      string query='select id, stageName,AccountId, Account.Rating from opportunity where stageName IN :strlist AND AccountId !=Null';
     system.debug('query=='+query);
     return Database.getQueryLocator(query); 
    }
     global Void execute(Database.BatchableContext bc, List<opportunity> Scope){
      
        for(opportunity o :Scope){
            o.Account.Rating='client';  
          system.debug('Rating'+o.Account.Rating);
            recordsProcessed = recordsProcessed + 1;
        }
         update Scope;}
         global void finish(Database.BatchableContext bc){
        System.debug(recordsProcessed + 'records processed. Shazam!');
        AsyncApexJob job = [SELECT Id, Status,NumberOfErrors,JobItemsProcessed,TotalJobItems, CreatedBy.Email 
                            FROM AsyncApexJob
                            WHERE Id = :bc.getJobId()];  
    }   
     }

@isTest
public class UpdateAccountRatingTest {
    @isTest
    public static void unit_test(){
       //insert All mandatory fields
        Account acc =new Account();
        acc.Name = 'test';
        acc.Rating='prospect';
        insert acc;
        
        //insert All mandatory fields
        Opportunity opp = new opportunity();
        opp.Name = 'test opp';
        opp.Accountid = acc.Id;
        opp.stageName = 'workInprogress';
        opp.CloseDate = system.today()+5;
        insert opp;
         
       
        
        Test.startTest();
      
        UpdateAccountRating uar  = new UpdateAccountRating();
        Database.executeBatch(uar);
      String sch = '0 0 0 1 * ? *';
      string JobID = system.schedule('BatchJob',sch, new UpdateAccountRatingSchedular());
        Test.stopTest();
       

 }
    }