use batch apex challange

1. Main Class
 public class LeadProcessor implements Database.Batchable<sObject> {
        public Database.QueryLocator start(Database.BatchableContext bc) {
            return Database.getQueryLocator(
                [SELECT Id, Name FROM Lead]
            );
        }
        public void execute(Database.BatchableContext bc, List<Lead> leads){
            for(Lead l: leads){
                 l.LeadSource = 'Dreamforce';
            }
            update leads;
        }
        public void finish(Database.BatchableContext bc){
            System.debug('Done');       
        }
    }
2. Test Class
@isTest
private class LeadProcessorTest {
	@isTest
    private static void testLeadProcessorBatch(){
        // Load Test Data
        List<Lead> leads = new List<Lead>();
        for(Integer i=0;i<=200;i++){
            leads.add(new Lead(LastName='LeadLstName', Company='SalesForce'));
        }
        insert leads;
        // perfor test 
        Test.startTest();
        LeadProcessor lp = new LeadProcessor();
        Id batchId = Database.executeBatch(lp,200);
        Test.stopTest();
        //check result
        List<Lead> updatedLeads = [SELECT Id FROM Lead WHERE LeadSource='Dreamforce'];
        System.assertEquals(200, updatedLeads.size(),'ERROR: at least 1 Lead record not updated correctly');
    }
}