[router] Introduce router integration tests (#10086)

sgl-router/py_test/integration/test_retries.py

@@ -0,0 +1,65 @@
+import concurrent.futures
+import subprocess
+import time
+
+import pytest
+import requests
+
+
+@pytest.mark.integration
+def test_retry_reroutes_to_healthy_worker(router_manager, mock_workers):
+    # Worker A always 500; Worker B healthy
+    # Worker A always 500; Worker B/C healthy
+    _, [url_a], [id_a] = mock_workers(n=1, args=["--status-code", "500"])  # fail
+    _, [url_b], [id_b] = mock_workers(n=1)
+    _, [url_c], [id_c] = mock_workers(n=1)
+    rh = router_manager.start_router(
+        worker_urls=[url_a, url_b, url_c],
+        policy="round_robin",
+        extra={
+            "retry_max_retries": 3,
+            "retry_initial_backoff_ms": 10,
+            "retry_max_backoff_ms": 50,
+        },
+    )
+
+    r = requests.post(
+        f"{rh.url}/v1/completions",
+        json={
+            "model": "test-model",
+            "prompt": "x",
+            "max_tokens": 1,
+            "stream": False,
+        },
+        timeout=5,
+    )
+    assert r.status_code == 200
+    wid = r.headers.get("X-Worker-Id") or r.json().get("worker_id")
+    assert wid == id_b  # should have retried onto healthy worker
+    # mock_workers fixture handles cleanup
+
+
+@pytest.mark.integration
+def test_disable_retries_surfaces_failure(router_manager, mock_workers):
+    # Single failing worker, retries disabled -> should return 500
+    _, [url], [wid] = mock_workers(n=1, args=["--status-code", "500"])  # always fail
+    rh = router_manager.start_router(
+        worker_urls=[url],
+        policy="round_robin",
+        extra={
+            "disable_retries": True,
+        },
+    )
+
+    r = requests.post(
+        f"{rh.url}/v1/completions",
+        json={
+            "model": "test-model",
+            "prompt": "x",
+            "max_tokens": 1,
+            "stream": False,
+        },
+        timeout=5,
+    )
+    assert r.status_code == 500
+    # mock_workers fixture handles cleanup