[ci][build] add tests for python only compilation (#10915)

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

tests/standalone_tests/lazy_torch_compile.py

@@ -0,0 +1,28 @@
+# Description: Test the lazy import module
+# 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
+
+module_name = "torch._inductor.async_compile"
+
+# 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(
+    lambda: module_name in sys.modules) 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 module_name not in sys.modules, (
+    f"Module {module_name} is imported. To see the first"
+    f" import location, run the test with `use_blame=True`.")