test_update_kwargs_does_not_mutate_defaults_and_merges_metadata

tests/litellm/test_router.py

@@ -0,0 +1,54 @@
+import copy
+import json
+import os
+import sys
+
+import pytest
+from fastapi.testclient import TestClient
+
+sys.path.insert(
+    0, os.path.abspath("../../..")
+)  # Adds the parent directory to the system path
+
+
+import litellm
+
+
+def test_update_kwargs_does_not_mutate_defaults_and_merges_metadata():
+    # initialize a real Router (env‑vars can be empty)
+    router = litellm.Router(
+        model_list=[
+            {
+                "model_name": "gpt-3.5-turbo",
+                "litellm_params": {
+                    "model": "azure/chatgpt-v-3",
+                    "api_key": os.getenv("AZURE_API_KEY"),
+                    "api_version": os.getenv("AZURE_API_VERSION"),
+                    "api_base": os.getenv("AZURE_API_BASE"),
+                },
+            }
+        ],
+    )
+
+    # override to known defaults for the test
+    router.default_litellm_params = {
+        "foo": "bar",
+        "metadata": {"baz": 123},
+    }
+    original = copy.deepcopy(router.default_litellm_params)
+    kwargs = {}
+
+    # invoke the helper
+    router._update_kwargs_with_default_litellm_params(
+        kwargs=kwargs,
+        metadata_variable_name="litellm_metadata",
+    )
+
+    # 1) router.defaults must be unchanged
+    assert router.default_litellm_params == original
+
+    # 2) non‑metadata keys get merged
+    assert kwargs["foo"] == "bar"
+
+    # 3) metadata lands under "metadata"
+    assert kwargs["litellm_metadata"] == {"baz": 123}