chore: import upstream snapshot with attribution

tests/unittests/models/test_litellm_import.py

@@ -0,0 +1,108 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import importlib.util
+import os
+import subprocess
+import sys
+
+import pytest
+
+
+def _subprocess_env() -> dict[str, str]:
+  env = dict(os.environ)
+  src_path = os.path.join(os.getcwd(), "src")
+  pythonpath = env.get("PYTHONPATH", "")
+  env["PYTHONPATH"] = (
+      f"{src_path}{os.pathsep}{pythonpath}" if pythonpath else src_path
+  )
+  return env
+
+
+def test_importing_models_does_not_import_litellm_or_set_mode():
+  env = _subprocess_env()
+  env.pop("LITELLM_MODE", None)
+
+  result = subprocess.run(
+      [
+          sys.executable,
+          "-c",
+          (
+              "import os, sys\n"
+              "import google.adk.models\n"
+              "print('litellm' in sys.modules)\n"
+              "print(os.environ.get('LITELLM_MODE'))\n"
+          ),
+      ],
+      check=True,
+      capture_output=True,
+      text=True,
+      env=env,
+  )
+  stdout_lines = result.stdout.strip().splitlines()
+  assert stdout_lines == ["False", "None"]
+
+
+def test_ensure_litellm_imported_defaults_to_production():
+  if importlib.util.find_spec("litellm") is None:
+    pytest.skip("litellm is not installed")
+
+  env = _subprocess_env()
+  env.pop("LITELLM_MODE", None)
+
+  result = subprocess.run(
+      [
+          sys.executable,
+          "-c",
+          (
+              "import os\n"
+              "from google.adk.models.lite_llm import"
+              " _ensure_litellm_imported\n"
+              "_ensure_litellm_imported()\n"
+              "print(os.environ.get('LITELLM_MODE'))\n"
+          ),
+      ],
+      check=True,
+      capture_output=True,
+      text=True,
+      env=env,
+  )
+  assert result.stdout.strip() == "PRODUCTION"
+
+
+def test_ensure_litellm_imported_does_not_override():
+  if importlib.util.find_spec("litellm") is None:
+    pytest.skip("litellm is not installed")
+
+  env = _subprocess_env()
+  env["LITELLM_MODE"] = "DEV"
+
+  result = subprocess.run(
+      [
+          sys.executable,
+          "-c",
+          (
+              "import os\n"
+              "from google.adk.models.lite_llm import"
+              " _ensure_litellm_imported\n"
+              "_ensure_litellm_imported()\n"
+              "print(os.environ.get('LITELLM_MODE'))\n"
+          ),
+      ],
+      check=True,
+      capture_output=True,
+      text=True,
+      env=env,
+  )
+  assert result.stdout.strip() == "DEV"