Mockito - how to answer with custom object

Trying to test the construction like this:

@RequestMapping(value = "/test", method = POST)
public ResponseEntity test(@RequestBody TestRequest request, Errors errors) {

    testValidator.validate(request, errors);

    if (errors.hasErrors())
        return new ResponseEntity(HttpStatus.BAD_REQUEST);

    return new ResponseEntity(HttpStatus.OK);
}

The Errors object is passed by framework and not by me, so there's no better way to change it's behaviour for the test except of using something like Mockito's Answer:

doAnswer(new Answer<Errors>() {

     @Override
     public Errors answer(InvocationOnMock invocation) throws Throwable {

         Errors errors = spy((Errors) invocation.getArguments()[1]);
         //errors.rejectValue("id", "id", "id rejected");

         doReturn(true).when(errors).hasErrors();

         return errors;
     }

}).when(testValidator).validate(any(), any());

ResponseEntity re = testRestTemplate
        .postForEntity("/test", new TestRequest(213L), String.class);

assertEquals(HttpStatus.BAD_REQUEST, re.getStatusCode());

... but the problem is errors.hasErrors() still returns false despite on doAnswer test block and the assertion fails because of HTTP status OK. I expect the Errors object will become the spy with specified behaviour right after .validate() call but seems I'm doing something wrong.

So, how to return a custom object using Mockito's doAnswer?