@Test
 public void testerIsStored() {
   trainerService.saveTraier(tester);
   long testerId = tester.getId();
   assertEquals(tester, trainerService.getTrainer(testerId));
 }
 @Override
 public void add(Trainer trainer) {
   trainer.setId(this.getNextId());
   this.database.put(trainer.getId(), trainer);
 }