[CI] Fix test_shared_storage_connector_hashes (vllm-project#25748)

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

Author: chaunceyjiang

tests/v1/kv_connector/unit/test_nixl_connector.py

@@ -26,6 +26,8 @@
 from vllm.distributed.kv_transfer.kv_connector.v1.nixl_connector import (
     KVConnectorRole, NixlAgentMetadata, NixlConnector, NixlConnectorMetadata,
     NixlConnectorWorker, NixlKVConnectorStats)
+from vllm.distributed.kv_transfer.kv_transfer_state import (
+    ensure_kv_transfer_shutdown, has_kv_transfer_group)
 from vllm.forward_context import ForwardContext
 from vllm.platforms.interface import Platform
 from vllm.sampling_params import SamplingParams
@@ -35,6 +37,26 @@
 from .utils import create_request, create_scheduler, create_vllm_config
 
 
+@pytest.fixture(scope="module", autouse=True)
+def clear_kv_transfer():
+    """
+    The test cases in this file use `VLLM_ENABLE_V1_MULTIPROCESSING=0`,
+    causing the global variable `_KV_CONNECTOR_AGENT` 
+    to be assigned but never deleted.
+
+    Since the current pytest process does not terminate and instead 
+    continues running tests from other files,
+    this global variable remains in memory and interferes 
+    with test cases in other modules.
+    
+    So we use this fixture to ensure that the global variable
+    `_KV_CONNECTOR_AGENT` is properly cleaned up after each test.
+    """
+    yield
+    if has_kv_transfer_group():
+        ensure_kv_transfer_shutdown()
+
+
 class FakeNixlWrapper:
     """Mock implementation of NixlWrapper for testing.