Testing validation constraints

Question

The Hibernate Validator documentation has a simple Getting Started guide which outlines testing validation rules.

The relevant chunk is

@Test
public void manufacturerIsNull() {
    Car car = new Car(null, "DD-AB-123", 4);

    Set<ConstraintViolation<Car>> constraintViolations =
        validator.validate(car);

    assertEquals(1, constraintViolations.size());
    assertEquals("may not be null", constraintViolations.iterator().next().getMessage());
}

It seems to me a fairly vague route to test if the NotNull constraint has been violated.

My simple solution would be something like

public static <T> boolean  containsConstraintViolation(
    Set<ConstraintViolation<T>> violations, Class<?> constraint) {

    for (ConstraintViolation<?> violation : violations) {
        ConstraintDescriptor<?> descriptor = violation.getConstraintDescriptor();
            if (constraint.isAssignableFrom(descriptor.getAnnotation().getClass()))
                return true;
        }
    return false;
}

Which allows me to do tests like

assertTrue(ValidationUtils.containsConstraintViolation(violations, NotNull.class));

However, I'm sure this is going to be naive in the long run and am wondering if there's not some other library or API I'm missing to assist in unit testing constraints.

Answer 1

You could have a look at the class org.hibernate.validator.test.util.TestUtil which is used for Hibernate Validator's own tests and offers functionality for testing expected constraint violations (amongst others there is assertCorrectConstraintTypes() for example).

Just note, that this class is not part of Hibernate Validator's public API, so it may be best to just use it to get some ideas.

When comparing error messages always be sure to have the VM's locale correctly set. Even better is to match against localized messages loaded via the correct resource bundle (org.hibernate.validator.ValidationMessages for the standard constraints in the case of Hibernate Validator).