### Question:
Services { public <S> S get(Class<S> service) { final S instance = getService(service); if (instance == null) { throw new LionEngineException(ERROR_SERVICE_GET + service.getName()); } return instance; } Services(); S create(Class<S> service); S add(S service); S get(Class<S> service); Optional<S> getOptional(Class<S> service);  }### Answer:
@Test void testNotFound() { final Services services = new Services(); assertThrows(() -> services.get(Camera.class), Services.ERROR_SERVICE_GET + Camera.class.getName()); }
@Test void testNull() { final Services services = new Services(); assertThrows(() -> services.get(null), "Unexpected null argument !"); }