[router] Introduce router integration tests (#10086)

sgl-router/py_test/integration/test_worker_management.py

@@ -0,0 +1,61 @@
+import collections
+import subprocess
+import time
+
+import pytest
+import requests
+
+
+@pytest.mark.integration
+def test_add_and_remove_worker(mock_worker, router_manager, mock_workers):
+    # Start with a single worker
+    proc1, url1, id1 = mock_worker
+    rh = router_manager.start_router(worker_urls=[url1], policy="round_robin")
+
+    # Add a second worker
+
+    procs2, urls2, ids2 = mock_workers(n=1)
+    url2 = urls2[0]
+    id2 = ids2[0]
+    router_manager.add_worker(rh.url, url2)
+
+    # Send some requests and ensure both workers are seen
+    seen = set()
+    with requests.Session() as s:
+        for i in range(20):
+            r = s.post(
+                f"{rh.url}/v1/completions",
+                json={
+                    "model": "test-model",
+                    "prompt": f"x{i}",
+                    "max_tokens": 1,
+                    "stream": False,
+                },
+            )
+            assert r.status_code == 200
+            wid = r.headers.get("X-Worker-Id") or r.json().get("worker_id")
+            seen.add(wid)
+            if len(seen) == 2:
+                break
+
+    assert id1 in seen and id2 in seen
+
+    # Now remove the second worker
+    router_manager.remove_worker(rh.url, url2)
+
+    # After removal, subsequent requests should only come from first worker
+    with requests.Session() as s:
+        for i in range(10):
+            r = s.post(
+                f"{rh.url}/v1/completions",
+                json={
+                    "model": "test-model",
+                    "prompt": f"y{i}",
+                    "max_tokens": 1,
+                    "stream": False,
+                },
+            )
+            assert r.status_code == 200
+            wid = r.headers.get("X-Worker-Id") or r.json().get("worker_id")
+            assert wid == id1
+    # mock_workers fixture handles cleanup