Add validation check for the return value of methods annotated with @Rule

[kcooney]

We should add a validation check that methods annotated with @Rule are public and return either a TestRule (or subclass) or a MethodRule (or subclass)

[kcooney]

Also, methods annotated with @Rule should not be static (unless they are also annotated with @ClassRule) and methods annotated with @ClassRule should be static

[npathai]

@kcooney All validations are already in place.
Tested following validations:

• @Rule methods must be public, non-static and return @TestRule or @MethodRule
• @ClassRule methods must be public and static and return @TestRule or @MethodRule

[npathai]

@kcooney But as with #589 same problem is present with @ClassRule. Should we create a new issue for that? But I am still unclear about the difference between TestRule and MethodRule. Do you have some idea as to why was MethodRule was un-deprecated in version 4.9?

[kcooney]

@NarendraPathai you can only use @ClassRule with TestRule.

BTW, MethodRule was un-deprecated because some developers preferred it over TestRule for rules that operate on methods.

[npathai]

@kcooney @ClassRule methods do allow MethodRule while validating, but do not call them. So should we change the validation? Because this case passes without validation error:

// should fail validation if @ClassRule does not allow `MethodRule`
    public class ClassRuleTest {
        @ClassRule
        public static MethodRule methodRule() {
            return new MethodRule() {

                @Override
                public Statement apply(Statement base, FrameworkMethod method, Object target) {
                    return base;
                }
            };
        }

        @Test
        public void doNothing() {

        }
    }

[kcooney]

@NarendraPathai we should certainly update the validation code for this. Class rules work on the class, so there is no method to pass to a MethodRule.

If you would like to work on this, note that we now support validating via annotations. See https://github.com/junit-team/junit/blob/master/src/main/java/org/junit/validator/AnnotationValidator.java We should simply update RuleMemberValidator. It's unfortunate that we have two separate ways to do validations, but I don't think we can fix this in the 4.x timeframe.

If you don't want to work on this, let's open a new bug so we can track it.

Thanks!