RFR: 8373272: Genshen: ShenandoahOldGenerationTest fails after JDK-8373056

[William Kemper]

On Mon, 8 Dec 2025 19:32:16 GMT, Xiaolong Peng <xpeng at openjdk.org> wrote:

> ShenandoahOldGeneration::configure_plab_for_current_thread has been updated to only handle plab req, which is a behavior change, but ShenandoahOldGenerationTest was not updated to match the behavior change, causing the test to fail.
> 
> The two failing unit tests of ShenandoahOldGenerationTest have been removed in this PR since the behavior being verified with them is no longer in configure_plab_for_current_thread, meanwhile one more unit test is added to verify the behavior of `expend_promoted`
> 
> ### Test
> - [x] CONF=macosx-aarch64-server-fastdebug make test TEST=gtest
> - [x] CONF=macosx-aarch64-server-fastdebug make test TEST=hotspot_gc_shenandoah

Thank you!

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Marked as reviewed by wkemper (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/28706#pullrequestreview-3554431253