From 066cc1883afe3a69a49638df4c8d7cfbc1fd0f2d Mon Sep 17 00:00:00 2001
From: Yuneng Jiang <yuneng@berri.ai>
Date: Fri, 18 Sep 2026 02:39:58 -0700
Subject: [PATCH] test(router): cover legacy lowest TPM selection

---
 .../router_strategy/test_lowest_tpm_rpm.py    | 54 +++++++++++++++++++
 1 file changed, 54 insertions(+)
 create mode 100644 tests/test_litellm/router_strategy/test_lowest_tpm_rpm.py

diff --git a/tests/test_litellm/router_strategy/test_lowest_tpm_rpm.py b/tests/test_litellm/router_strategy/test_lowest_tpm_rpm.py
new file mode 100644
index 00000000000..7b13b196d5b
--- /dev/null
+++ b/tests/test_litellm/router_strategy/test_lowest_tpm_rpm.py
@@ -0,0 +1,54 @@
+from datetime import datetime, timedelta
+from typing import Final
+
+from litellm import Router
+from litellm.types.router import DeploymentTypedDict, LiteLLMParamsTypedDict
+
+MODEL_GROUP: Final = "lowest-tpm-router"
+HIGH_USAGE_DEPLOYMENT_ID: Final = "highest-usage"
+LOW_USAGE_DEPLOYMENT_ID: Final = "lowest-usage"
+
+
+def _deployment(deployment_id: str) -> DeploymentTypedDict:
+    params: LiteLLMParamsTypedDict = {
+        "model": "gpt-4o",
+        "api_key": "key",
+        "mock_response": f"from {deployment_id}",
+    }
+    return {
+        "model_name": MODEL_GROUP,
+        "litellm_params": params,
+        "model_info": {"id": deployment_id},
+    }
+
+
+def test_usage_based_routing_v1_selects_the_lowest_recorded_tpm() -> None:
+    router: Final = Router(
+        model_list=[
+            _deployment(HIGH_USAGE_DEPLOYMENT_ID),
+            _deployment(LOW_USAGE_DEPLOYMENT_ID),
+        ],
+        routing_strategy="usage-based-routing",
+        num_retries=0,
+    )
+    usage_by_deployment: Final = {
+        HIGH_USAGE_DEPLOYMENT_ID: 100,
+        LOW_USAGE_DEPLOYMENT_ID: 1,
+    }
+    now: Final = datetime.now()
+    cache_keys: Final = tuple(
+        f"{MODEL_GROUP}:tpm:{(now + timedelta(minutes=offset)).strftime('%H-%M')}"
+        for offset in range(60)
+    )
+
+    for cache_key in cache_keys:
+        router.cache.set_cache(
+            key=cache_key, value=usage_by_deployment, ttl=float("inf")
+        )
+
+    deployment: Final = router.get_available_deployment(
+        model=MODEL_GROUP,
+        messages=[{"role": "user", "content": "test"}],
+    )
+
+    assert deployment["model_info"]["id"] == LOW_USAGE_DEPLOYMENT_ID