Sample Batch job along with test class

AccountUpdateBatchJob

global class AccountUpdateBatchJob implements Database.Batchable<sObject> 
{
    global Database.QueryLocator start(Database.BatchableContext BC) 
    {
        String query = 'SELECT Id,Name FROM Account';
        
        return Database.getQueryLocator(query);
    }
    global void execute(Database.BatchableContext BC, List<Account> scope) 
    {
        for(Account a : scope)
        {
            a.Name = a.Name + 'Updated by Batch job';
        }
        update scope;
    }
    global void finish(Database.BatchableContext BC) {
    }
}

AccountUpdateBatchJobTest

@isTest 
public class AccountUpdateBatchJobTest 
{
    static testMethod void testMethod1() 
    {
        List<Account> lstAccount= new List<Account>();
        for(Integer i=0 ;i <200;i++)
        {
            Account acc = new Account();
            acc.Name ='Name'+i;
            lstLead.add(acc);
        }
        
        insert lstAccount;
        
        Test.startTest();

            AccountUpdateBatchJob obj = new AccountUpdateBatchJob();
            DataBase.executeBatch(obj); 
            
        Test.stopTest();
    }
}