@Test
public void invalidParametersPreparationIdNoOperations() {

    // given parameters with a preparation preparation id
    AggregationParameters parameters = new AggregationParameters();
    parameters.setPreparationId("prep#1234");
    // when
    Set<ConstraintViolation<AggregationParameters>> constraintViolations = validator.validate(parameters);
    // then 2 violations (operations and groupBy are empty)
    Assert.assertEquals(2, constraintViolations.size());
}