[router] Introduce router integration tests (#10086)

sgl-router/py_test/integration/test_service_discovery_shim.py

@@ -0,0 +1,36 @@
+import pytest
+import requests
+
+
+@pytest.mark.integration
+def test_discovery_shim_add_remove(router_manager, mock_workers):
+    # Start router without workers
+    rh = router_manager.start_router(worker_urls=[], policy="round_robin")
+
+    # Initially empty
+    urls = router_manager.list_workers(rh.url)
+    assert urls == []
+
+    # Add a worker (simulate discovery event)
+    _, [wurl], [wid] = mock_workers(n=1)
+    router_manager.add_worker(rh.url, wurl)
+    urls = router_manager.list_workers(rh.url)
+    assert wurl in urls
+
+    # Can serve a request
+    r = requests.post(
+        f"{rh.url}/v1/completions",
+        json={
+            "model": "test-model",
+            "prompt": "hi",
+            "max_tokens": 1,
+            "stream": False,
+        },
+    )
+    assert r.status_code == 200
+
+    # Remove worker (simulate pod deletion)
+    router_manager.remove_worker(rh.url, wurl)
+    urls = router_manager.list_workers(rh.url)
+    assert wurl not in urls
+    # mock_workers fixture handles cleanup