[CI] Keep vLLM log propagation on through the first LLM init in caplog_vllm (#61535)

Signed-off-by: khluu <khluu000@gmail.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Bugen Zhao <i@bugenzhao.com>

tests/conftest.py

@@ -1406,14 +1406,15 @@ def vllm_runner():
 
 
 @pytest.fixture()
-def temporary_enable_log_propagate():
+def temporary_enable_log_propagate(monkeypatch):
     import logging
 
-    logger = logging.getLogger("vllm")
-    previous_propagate = logger.propagate
-    logger.propagate = True
-    yield
-    logger.propagate = previous_propagate
+    from vllm.logger import DEFAULT_LOGGING_CONFIG
+
+    # The first LLM init in a process reapplies DEFAULT_LOGGING_CONFIG, which
+    # would otherwise turn propagation back off mid-test.
+    monkeypatch.setitem(DEFAULT_LOGGING_CONFIG["loggers"]["vllm"], "propagate", True)
+    monkeypatch.setattr(logging.getLogger("vllm"), "propagate", True)
 
 
 @pytest.fixture()

tests/entrypoints/multimodal/llm/test_mm_cache_external_injection.py

@@ -69,7 +69,6 @@ def test_inject_into_mm_cache(
     mm_processor_cache_type,
     caplog_vllm,
     vllm_runner,
-    monkeypatch,
 ):
     """Test that inject_into_mm_cache() injects pre-processed mm_kwargs into
     the processor cache and MM cache hit metrics are updated correctly.
@@ -88,9 +87,6 @@ def test_inject_into_mm_cache(
         limit_mm_per_prompt={"image": 2},
         mm_processor_cache_type=mm_processor_cache_type,
     ) as runner:
-        # The first LLM initialization can reset logger propagation.
-        monkeypatch.setattr(logging.getLogger("vllm"), "propagate", True)
-
         # Step 1: Normal requests to populate the cache
         runner.llm.chat(_make_messages(image_urls[0]))
         assert _get_mm_cache_stats(runner.llm.get_metrics()) == (1, 0)