code: @Test public void testConstraintViolationException(){
    ConstraintViolationException violationException=mock(ConstraintViolationException.class);
    ConstraintViolation violation=mock(ConstraintViolation.class,Answers.RETURNS_DEEP_STUBS);
    given(violationException.getConstraintViolations()).willReturn(Sets.<ConstraintViolation<?>>newSet(violation));
    RpcException rpcException=new RpcException("violation",violationException);
    Response response=exceptionMapper.toResponse(rpcException);
    assertThat(response,not(nullValue()));
    assertThat(response.getEntity(),instanceOf(ViolationReport.class));
  }
  