@IsTest
public class testclassownerassignmanager{
    static testmethod void metest()
    {
        Profile pro = [SELECT Id FROM Profile WHERE Name='Standard User']; 
        
        //Creating testUserA who acts as Manager for another User
        User testUserA = new User(
            Alias = 'standard', Email='standarduser@testorg.com',  
            EmailEncodingKey='UTF-8', LastName='Testing', LanguageLocaleKey='en_US', 
            LocaleSidKey='en_US', ProfileId = pro.Id, 
            TimeZoneSidKey='America/Los_Angeles',
            UserName='testUserA@testorganise.com'); 
        insert testUserA ;

		//Creating testUserB whose manager is testUserA - This user creates few accounts and becomes Inactive
        User testUserB = new User(
            Alias = 'standard', Email='standarduser@testorg.com',  
            EmailEncodingKey='UTF-8', LastName='Testing', LanguageLocaleKey='en_US', 
            LocaleSidKey='en_US', ProfileId = pro.Id,  
            TimeZoneSidKey='America/Los_Angeles', 
            UserName='testUserB@testorganise.com'); 
        testUserB.ManagerID = testUserA.id;
        insert testUserB;
        
        //Insering few Accounts whose Owner is testUserB
        List<Account> acclist= new List<Account>();
        System.runAs (testUserA){
            
            for(Integer i=0;i<=10;i++)
            {
                account a = new account(Name='Test' + i, ownerid=testUserB.id);
                acclist.add(a);
            }
            Insert acclist;
        }
        
        //Inactivate testUserB so that the accounts owner is changed to testUserB's manager i.e, testUserA
        test.starttest();
        testUserB.IsActive = false;
        update testUserB;
        test.stoptest();
          
        Account a = [select id, name, OwnerId from Account where ID IN: acclist limit 1];
        system.assertEquals(a.ownerid, testUserB.Managerid);
    }
}