[Router][CI/CD and misc.] Add RoundRobinRouter logic testing (#639)

* added basic unit test for RoundRobinRouter route_request logic

Signed-off-by: Lucas Tucker <[email protected]>

* address gemini concerns

Signed-off-by: Lucas Tucker <[email protected]>

---------

Signed-off-by: Lucas Tucker <[email protected]>
Co-authored-by: Lucas Tucker <[email protected]>
Co-authored-by: Yuhan Liu <[email protected]>

Author: 3 people

src/tests/test_roundrobin_router.py

@@ -0,0 +1,74 @@
+import random
+from typing import Dict, List, Tuple
+
+from vllm_router.routers.routing_logic import RoundRobinRouter
+
+
+class EndpointInfo:
+    def __init__(self, url: str):
+        self.url = url
+
+
+class RequestStats:
+    def __init__(self, qps: float):
+        self.qps = qps
+
+
+class Request:
+    def __init__(self, headers: Dict[str, str]):
+        self.headers = headers
+
+
+class EngineStats:
+    def __init__(self):
+        return
+
+
+def generate_request_args(
+    num_endpoints: int, qps_range: int = 0
+) -> Tuple[List[EndpointInfo], Dict[str, EngineStats], Dict[str, RequestStats]]:
+    endpoints = [
+        EndpointInfo(
+            url=f"{endpoint_index}",
+        )
+        for endpoint_index in range(num_endpoints)
+    ]
+    engine_stats = {
+        f"{endpoint_index}": EngineStats() for endpoint_index in range(num_endpoints)
+    }
+    request_stats = {
+        f"{endpoint_index}": RequestStats(qps=random.uniform(0, qps_range))
+        for endpoint_index in range(num_endpoints)
+    }
+    return endpoints, engine_stats, request_stats
+
+
+def generate_request(request_type="http") -> Request:
+    return Request({"type": request_type})
+
+
+def test_roundrobin_logic(
+    dynamic_discoveries: int = 10, max_endpoints: int = 1000, max_requests: int = 10000
+):
+    """
+    Ensure that all active urls have roughly same number of requests (difference at most 1)
+    """
+    router = RoundRobinRouter()
+
+    def _fixed_router_check(num_endpoints: int, num_requests: int) -> bool:
+        # Make num_requests requests to the router and check even output distribution
+        endpoints, engine_stats, request_stats = generate_request_args(num_endpoints)
+        output_distribution = {}
+        for request_idx in range(num_requests):
+            request = generate_request()
+            url = router.route_request(endpoints, engine_stats, request_stats, request)
+            output_distribution[url] = output_distribution.get(url, 0) + 1
+        request_counts = output_distribution.values()
+        return max(request_counts) - min(request_counts) <= 1
+
+    for _ in range(dynamic_discoveries):
+        num_endpoints = random.randint(1, max_endpoints)
+        num_requests = random.randint(1, max_requests)
+        # Perform router check
+        res = _fixed_router_check(num_endpoints, num_requests)
+        assert res