[Test] add unit test for skipping already preempted request

[glenliu21]

Motivation

Addressing bullet 4 of #13470.

Checklist

• Format your code according to the Format code with pre-commit.
• Add unit tests according to the Run and add unit tests.
• Follow the SGLang code style guidance.

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[gemini-code-assist]

Summary of Changes

Hello @glenliu21, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new unit test to validate the scheduler's preemption logic. The test specifically ensures that the system avoids re-preempting requests that have already been marked for preemption, thereby preventing redundant operations and ensuring efficient resource management during scheduling.

Highlights

• New Unit Test: Added test_preempt_skip_already_preempted_request to verify that the preemption mechanism correctly skips requests that have already been preempted when attempting to free up tokens for new requests.

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Changelog

• test/registered/scheduler/test_prefill_adder.py
  • Added a new test case test_preempt_skip_already_preempted_request to verify the scheduler's behavior when handling already preempted requests.

Activity

• No specific activity (comments, reviews, or progress updates) was provided in the context.

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[gemini-code-assist]

Code Review

This pull request adds a unit test for the preemption logic in the scheduler. The new test case, test_preempt_skip_already_preempted_request, correctly verifies that a request already marked for preemption is not considered for preemption again. The test is well-structured and the assertions are clear. I have one suggestion to improve the test's robustness by using unique request IDs.

[Kangyan-Zhou]

/rerun-stage stage-b-test-small-1-gpu

[github-actions]

✅ Triggered stage-b-test-small-1-gpu to run independently (skipping dependencies).

[github-actions]

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