[ci] add vllm_test_utils (#10659)

Signed-off-by: youkaichao <youkaichao@gmail.com>

tests/entrypoints/llm/test_lazy_outlines.py

@@ -1,12 +1,12 @@
 import sys
 
+from vllm_test_utils import blame
+
 from vllm import LLM, SamplingParams
 from vllm.distributed import cleanup_dist_env_and_memory
 
 
-def test_lazy_outlines(sample_regex):
-    """If users don't use guided decoding, outlines should not be imported.
-    """
+def run_normal():
     prompts = [
         "Hello, my name is",
         "The president of the United States is",
@@ -25,13 +25,12 @@ def test_lazy_outlines(sample_regex):
         generated_text = output.outputs[0].text
         print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")
 
-    # make sure outlines is not imported
-    assert 'outlines' not in sys.modules
-
     # Destroy the LLM object and free up the GPU memory.
     del llm
     cleanup_dist_env_and_memory()
 
+
+def run_lmfe(sample_regex):
     # Create an LLM with guided decoding enabled.
     llm = LLM(model="facebook/opt-125m",
               enforce_eager=True,
@@ -51,5 +50,15 @@ def test_lazy_outlines(sample_regex):
         generated_text = output.outputs[0].text
         print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")
 
+
+def test_lazy_outlines(sample_regex):
+    """If users don't use guided decoding, outlines should not be imported.
+    """
     # make sure outlines is not imported
-    assert 'outlines' not in sys.modules
+    module_name = "outlines"
+    with blame(lambda: module_name in sys.modules) as result:
+        run_normal()
+        run_lmfe(sample_regex)
+    assert not result.found, (
+        f"Module {module_name} is already imported, the"
+        f" first import location is:\n{result.trace_stack}")