test: add test for get_router_model_info with Deployment object

Verifies that get_router_model_info accepts a Deployment object directly
and properly handles the LiteLLM_Params isinstance check.

tests/router_unit_tests/test_router_helper_utils.py

@@ -2198,3 +2198,33 @@ def test_get_valid_args():
     # Verify it contains keyword-only arguments too
     # These are common Router.__init__ parameters
     assert "assistants_config" in valid_args or "search_tools" in valid_args
+
+
+def test_get_router_model_info_with_deployment_object():
+    """Test get_router_model_info accepts Deployment object directly and reuses LiteLLM_Params"""
+    router = Router(
+        model_list=[
+            {
+                "model_name": "gpt-4",
+                "litellm_params": {"model": "gpt-4", "api_key": "test-key"},
+                "model_info": {"id": "test-id"},
+            }
+        ]
+    )
+
+    # Get the Deployment object (not dict)
+    deployment = router.get_deployment(model_id="test-id")
+    assert deployment is not None
+    assert isinstance(deployment, Deployment)
+    assert isinstance(deployment.litellm_params, LiteLLM_Params)
+
+    # Pass Deployment directly (not .model_dump()) - this exercises the isinstance check
+    # that reuses the existing LiteLLM_Params instead of reconstructing it
+    model_info = router.get_router_model_info(
+        deployment=deployment,
+        received_model_name="gpt-4",
+    )
+
+    # Verify we got valid model info back
+    assert model_info is not None
+    assert isinstance(model_info, dict)