[V1] V1 Enablement Oracle (#13726)

Signed-off-by: rshaw@neuralmagic.com <rshaw@neuralmagic.com>
Co-authored-by: rshaw@neuralmagic.com <rshaw@neuralmagic.com>
Co-authored-by: Nicolò Lucchesi <nlucches@redhat.com>
Co-authored-by: Tyler Michael Smith <tyler@neuralmagic.com>
Co-authored-by: Michael Goin <michael@neuralmagic.com>

tests/async_engine/test_async_llm_engine.py

@@ -151,6 +151,10 @@ def uid() -> str:
 
 @pytest_asyncio.fixture(scope="module")
 async def async_engine():
+    # We cannot use monkeypatch since this is a module
+    # scoped fixture and monkeypatch is function scoped.
+    previous_value = os.getenv("VLLM_USE_V1", None)
+    os.environ["VLLM_USE_V1"] = "0"
     engine = await asyncio.get_event_loop().run_in_executor(executor=None,
                                                             func=start_engine)
     try:
@@ -161,6 +165,11 @@ async def async_engine():
         await asyncio.sleep(0.1)
         cleanup_dist_env_and_memory()
 
+        if previous_value:
+            os.environ["VLLM_USE_V1"] = previous_value
+        else:
+            del os.environ["VLLM_USE_V1"]
+
 
 @pytest.fixture()
 def should_do_global_cleanup_after_test(request) -> bool: