Question from the Drupal 8 test

drupal_set_message(t('Candidate %firstname %lastname was added.', ['%firstname' => $firstname, '%lastname' => $lastname]));

drupal_set_message($this->t('Candidate %firstname %lastname was added.', ['%firstname' => $firstname, '%lastname' => $lastname]));

drupal_set_message(t('Candidate ' . $firstname . ' ' . $lastname . ' was added.'));

drupal_set_message($this->t('Candidate !firstname !lastname was added.', array('!firstname' => $firstname, '!lastname' => $lastname)));

drupal_set_message(t('Candidate %firstname %lastname was added.', array('%firstname' => $firstname, '%lastname' => $lastname)));

drupal_set_message($this->t('Candidate ' . $firstname . ' ' . $lastname . ' was added.'));