MultiValidationBean bean = new MultiValidationBean();
        bean.setRequiredCron(null); // Violates NotNull

        Set<ConstraintViolation<MultiValidationBean>> violations = validator.validate(bean);
        assertEquals(1, violations.size()); // Only NotNull violation

        bean.setRequiredCron("invalid"); // Now violates CronExpression
        violations = validator.validate(bean);