[CI] Fix ngram & suffix test oom

[fluctlux]

What this PR does / why we need it?

Avoid oom during CI by using with VllmRunner instead of LLM(), and enable test_ngram_correctness

How was this patch tested?

Before:

After:

CI passed.

• vLLM version: v0.12.0
• vLLM main: vllm-project/vllm@ad32e3e

[gemini-code-assist]

Code Review

This pull request aims to fix an Out-Of-Memory (OOM) error in CI for ngram and suffix tests. The changes involve replacing direct LLM instantiation with the VllmRunner context manager, which ensures proper resource cleanup. Additionally, the multiprocessing start method is set to 'spawn' to avoid issues with NPU context inheritance. The test test_ngram_correctness is also re-enabled.

The changes are logical and address the OOM issue effectively. My main feedback is regarding how the environment variable is set. Using os.environ at the module level can introduce side effects to other tests. I've suggested a more robust approach using pytest's monkeypatch fixture to scope the change correctly.

[gemini-code-assist]

Modifying os.environ directly at the module level can lead to side effects in other tests, as it's a global state change that persists throughout the pytest session. This can make tests flaky and hard to debug.

A safer and more idiomatic pytest approach is to use the monkeypatch fixture to manage environment variables. This ensures that the change is properly scoped and cleaned up after the tests in this module are done.

You could define a module-scoped autouse fixture like this, which would replace the direct modification of os.environ:

import pytest

@pytest.fixture(scope="module", autouse=True)
def set_spawn_method(monkeypatch):
    monkeypatch.setenv("VLLM_WORKER_MULTIPROC_METHOD", "spawn")

This would make the test suite more robust against side-effects.

[github-actions]

👋 Hi! Thank you for contributing to the vLLM Ascend project. The following points will speed up your PR merge:‌‌

• A PR should do only one thing, smaller PRs enable faster reviews.
• Every PR should include unit tests and end-to-end tests ‌to ensure it works and is not broken by other future PRs.
• Write the commit message by fulfilling the PR description to help reviewer and future developers understand.

If CI fails, you can run linting and testing checks locally according Contributing and Testing.

[wangxiyuan]

Hope the test can works now

[wangxiyuan]

really nice change. Thanks very much！！