RFR: 8376698: Add Spliterator tests for TreeMap sub-maps [v2]

[Chen Liang]

On Thu, 19 Feb 2026 09:35:00 GMT, Oli Gillespie <ogillespie at openjdk.org> wrote:

>> Add missing cases to SpliteratorTraversingAndSplittingTest. This came up when I was fixing https://bugs.openjdk.org/browse/JDK-8372946, and I noticed the tests do not cover these sub-maps.
>> 
>> Two interesting parts:
>> 
>> 1. These tests failed when first added because `SubMapKeyIterator` and `DescendingSubMapKeyIterator` do not eagerly throw `NullPointerException` for `null` action arguments. The spec says "Throws: NullPointerException - if the specified action is null", so I updated the implementation to match other spliterators.
>> 2. Since the descending maps have the reverse expected iteration order, I added support in the test harness for descending maps.
>
> Oli Gillespie has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:
> 
>  - Update copyright
>  - Merge remote-tracking branch 'origin/master' into spliterator-test
>  - Switch to Objects.requireNonNull
>  - Add tests and fix impl

The copyright year update and release note update look good to me.

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Marked as reviewed by liach (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/29485#pullrequestreview-3826335209