refactor: address bot review suggestions

- Simplify tracing.py by removing isinstance check (always enum now)
- Refactor test assertions to use dictionary mapping instead of if/elif
- Reduce code duplication and improve readability

Addresses Gemini Code Assist bot suggestions:
- tracing.py: Direct .name access since finish_reason is always enum
- test_litellm.py: Dictionary mapping for cleaner test assertions

Author: aperepel

src/google/adk/telemetry/tracing.py

@@ -303,11 +303,8 @@ def trace_call_llm(
           llm_response.usage_metadata.candidates_token_count,
       )
   if llm_response.finish_reason:
-    if isinstance(llm_response.finish_reason, types.FinishReason):
-      finish_reason_str = llm_response.finish_reason.name.lower()
-    else:
-      # Defensive fallback for string values (should never occur - all values mapped to enum)
-      finish_reason_str = str(llm_response.finish_reason).lower()
+    # finish_reason is always FinishReason enum
+    finish_reason_str = llm_response.finish_reason.name.lower()
     span.set_attribute(
         'gen_ai.response.finish_reasons',
         [finish_reason_str],

tests/unittests/models/test_litellm.py

@@ -1967,17 +1967,16 @@ async def test_finish_reason_propagation(
 
   async for response in lite_llm_instance.generate_content_async(llm_request):
     assert response.content.role == "model"
-    # Verify finish_reason is mapped to FinishReason enum, not raw string
+    # Verify finish_reason is mapped to FinishReason enum
     assert isinstance(response.finish_reason, types.FinishReason)
-    # Verify correct enum mapping
-    if finish_reason == "length":
-      assert response.finish_reason == types.FinishReason.MAX_TOKENS
-    elif finish_reason == "stop":
-      assert response.finish_reason == types.FinishReason.STOP
-    elif finish_reason == "tool_calls":
-      assert response.finish_reason == types.FinishReason.STOP
-    elif finish_reason == "content_filter":
-      assert response.finish_reason == types.FinishReason.SAFETY
+    # Verify correct enum mapping using dictionary
+    expected_mapping = {
+        "length": types.FinishReason.MAX_TOKENS,
+        "stop": types.FinishReason.STOP,
+        "tool_calls": types.FinishReason.STOP,
+        "content_filter": types.FinishReason.SAFETY,
+    }
+    assert response.finish_reason == expected_mapping[finish_reason]
     if expected_content:
       assert response.content.parts[0].text == expected_content
     if has_tool_calls: