RFR: 8376698: Add Spliterator tests for TreeMap sub-maps

[Chen Liang]

On Thu, 29 Jan 2026 20:29:43 GMT, Roger Riggs <rriggs 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.
>
> src/java.base/share/classes/java/util/TreeMap.java line 2141:
> 
>> 2139:             }
>> 2140:             public void forEachRemaining(Consumer<? super K> action) {
>> 2141:                 Objects.requireNonNull(action);
> 
> Is there a test for NPE action on an empty Map?

The new cases for subMap in SpliteratorTraversingAndSplittingTest should be sufficient.

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PR Review Comment: https://git.openjdk.org/jdk/pull/29485#discussion_r2743414552