In below code snippet in Salesforce, what is going wrong?

In below code snippet,

trigger TestBeforeDelete on Lead (before Delete) {

    for(Lead l : Trigger.Old)
    {
        l.addError('error');
    }

    String msgBody = 'Test Email';
    String Subject = 'Test from Cogni Force on Lead';
    Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
    String[] toAddresses = new String[] {'[email protected]'};
    mail.setToAddresses(toAddresses);
    mail.setReplyTo('[email protected]');
    mail.setSenderDisplayName('Cogniforce Test Simulator');
    mail.setSubject(Subject);
    mail.setPlainTextBody(msgBody);
    mail.setHTMLBody(msgBody);
    Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });
}

What is your observation and what is going wrong?