@Test
 public void onException() {
   // Mock: request
   HttpServletRequest request = mock(HttpServletRequest.class);
   // Mock: error handler
   when(errorHandler.handleError(
           any(HttpServletRequest.class), any(Locale.class), any(Exception.class)))
       .thenReturn(new ErrorMessage("xxx", "Error message"));
   // Call
   ResponseEntity<String> entity =
       get.onException(request, Locale.ENGLISH, new ApplicationNotFoundException(APP));
   assertNotNull(entity);
   assertEquals(
       "An error has occurred.\nMessage: Error message\nReference: xxx", entity.getBody());
   assertEquals(HttpStatus.INTERNAL_SERVER_ERROR, entity.getStatusCode());
 }