improve lazy import test (#30733)

Signed-off-by: Boyuan Feng <boyuan@meta.com>

tests/standalone_tests/lazy_imports.py

@@ -5,9 +5,6 @@
 # The utility function cannot be placed in `vllm.utils`
 # this needs to be a standalone script
 import sys
-from contextlib import nullcontext
-
-from vllm_test_utils import BlameResult, blame
 
 # List of modules that should not be imported too early.
 # Lazy import `torch._inductor.async_compile` to avoid creating
@@ -16,26 +13,10 @@ from vllm_test_utils import BlameResult, blame
 # `cv2` can easily mess up the environment.
 module_names = ["torch._inductor.async_compile", "cv2"]
 
+# set all modules in `module_names` to be None.
+# if we import any modules during `import vllm`, there would be a
+# hard error and nice stacktrace on the first import.
+for module_name in module_names:
+    sys.modules[module_name] = None  # type: ignore[assignment]
 
-def any_module_imported():
-    return any(module_name in sys.modules for module_name in module_names)
-
-
-# In CI, we only check finally if the module is imported.
-# If it is indeed imported, we can rerun the test with `use_blame=True`,
-# which will trace every function call to find the first import location,
-# and help find the root cause.
-# We don't run it in CI by default because it is slow.
-use_blame = False
-context = blame(any_module_imported) if use_blame else nullcontext()
-with context as result:
-    import vllm  # noqa
-
-if use_blame:
-    assert isinstance(result, BlameResult)
-    print(f"the first import location is:\n{result.trace_stack}")
-
-assert not any_module_imported(), (
-    f"Some the modules in {module_names} are imported. To see the first"
-    f" import location, run the test with `use_blame=True`."
-)
+import vllm  # noqa