public class SendEmailToContacts implements Database.Batchable<sObject> {
    public Database.QueryLocator start(Database.BatchableContext bc) {
        return Database.getQueryLocator('SELECT id,Email,LeadSource FROM Contact Where LastModifiedDate = today  ORDER By LastModifiedDate  DESC');
    }
    public void execute(Database.BatchableContext bc, List<Contact> records){
        list<String> Addresses = new list<String>();
        for(Contact Con : records){
            if(Con.LeadSource == 'Web' || Con.LeadSource == 'Phone Inquiry'){
                Addresses.add(Con.Email);
            }
        }
         Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();

       mail.setToAddresses(Addresses);
        mail.setSubject('Test subject');
        mail.setPlainTextBody('Sample body');
       
        Messaging.SendEmailResult[] results = Messaging.sendEmail(
                                 new Messaging.SingleEmailMessage[] { mail });
    }
    public void finish(Database.BatchableContext bc){
        Id job = bc.getJobId();
    }
}

Test Class

@IsTest
public class SendEmailToContactsTest {
  @isTest    
    public static void testit() {
      
       list<Contact>lstCon = new  list<Contact>();
        list<Contact>lstConu = new  list<Contact>();
        for(integer i = 0;i<5;i++){
            Contact l = new Contact();
            l.LastName = 'name';
            l.Email ='test'+i+'@test.com';
            lstCon.Add(l);
        }

        insert lstCon;
        for(Contact con : lstCon){
            con.leadSource = 'web';
           lstConu.Add(Con);
        }
        update lstConu;
       
            SendEmailToContacts lp = new SendEmailToContacts();
        Id batchId = Database.executeBatch(lp);
    }

}