NUTCH-3145 Upgrade to JUnit 6

[lewismc]

This is a PR for NUTCH-3145. It is quite an interesting issue as JUnit 6 requires Java 17. I am not convinced/sure that we want to orchestrate an upgrade from Java 11 --> 17 through a JUnit upgrade. I opened this ticket as a bit of an experiment. It also encouraged me to check in on NUTCH-2987 and perhaps more importantly the behemoth that is HADOOP-17177.
Any feedback or thoughts welcome. Thank you

[sebastian-nagel]

I'd be conservative and would not yet force users to require Java 17 as runtime, esp. given that is not yet 100% supported by Hadoop. A backward-compatible approach, similar to that described in HADOOP-18887 might be better.

What about?

• Require Java 17 to build Nutch, resp. run the unit tests.
• But still allow a Java 11 runtime by setting javac.version=11. The binary package would then still run on Java 11.

This option seems to work (I tried it, but without exhaustive testing).

[lewismc]

Yes I agree with you @sebastian-nagel I'm not keen to force a JDK upgrade to 17 via this PR either. I'll augment the PR accordingly. Thanks for the review.

[lewismc]

I augmented the CI to accommodate the backward-compatible Java version strategy for Apache Nutch, similar to the approach described in HADOOP-18887.
Key principle:

• Build requirement: Java 17+ (required by JUnit 6)
• Runtime compatibility: Java 11+ (bytecode target)

[lewismc]

Resolved conflicts. I'm wondering whether we should perform a separaste upgrade to JDK17 BEFORE we consider this branch further. It would certainly simpligy the CI as we wouldn't need to worry about the additional complexity it adds to the GitHub CI. I'm open to suggestions and would also like to respect the opinuons shared on dev@.