Fix EventPublisherFactory logic for disabled KV cache events (#27419)

Signed-off-by: Bradley <bradley.b.pitt@gmail.com>

tests/distributed/test_events.py

@@ -263,3 +263,52 @@ def test_data_parallel_rank_tagging(publisher_config):
         pub_1.shutdown()
         sub_0.close()
         sub_1.close()
+
+
+def test_event_publisher_factory():
+    """Test event publisher factory creation behavior under different configurations"""
+    from vllm.config.kv_events import KVEventsConfig
+    from vllm.distributed.kv_events import ZmqEventPublisher
+
+    # test config is None
+    publisher = EventPublisherFactory.create(None, DP_RANK)
+    assert isinstance(publisher, NullEventPublisher)
+    publisher.shutdown()
+
+    # test disable kv cache events
+    config = KVEventsConfig(
+        enable_kv_cache_events=False,
+        publisher="zmq",  # Even if zmq is specified, should return NullEventPublisher
+        endpoint="tcp://localhost:5557",
+    )
+    publisher = EventPublisherFactory.create(config, DP_RANK)
+    assert isinstance(publisher, NullEventPublisher)
+    publisher.shutdown()
+
+    # test zmq publisher
+    config = KVEventsConfig(
+        enable_kv_cache_events=True,
+        publisher="zmq",
+        endpoint="inproc://test-factory-true",
+    )
+    publisher = EventPublisherFactory.create(config, DP_RANK)
+    assert isinstance(publisher, ZmqEventPublisher)
+    publisher.shutdown()
+
+    # test unknown publisher
+    with pytest.raises(ValueError, match="Input should be"):
+        KVEventsConfig(
+            enable_kv_cache_events=True,
+            publisher="unknown_publisher",
+            endpoint="tcp://localhost:5557",
+        )
+
+    # test publisher not specified
+    config = KVEventsConfig(
+        enable_kv_cache_events=True,
+        # publisher not specified, should default to "zmq"
+        endpoint="tcp://localhost:5557",
+    )
+    publisher = EventPublisherFactory.create(config, DP_RANK)
+    assert isinstance(publisher, ZmqEventPublisher)
+    publisher.shutdown()