Add tests for file search edge cases to achieve 100% coverage

Add two tests to cover missing branches in file search streaming handler:
- test_google_model_file_search_empty_grounding_chunks: Tests when
  grounding_chunks is empty/None
- test_google_model_file_search_empty_retrieved_contexts: Tests when
  retrieved_contexts is empty (grounding_chunks exist but have no
  retrieved_context)

These tests follow the existing pattern of mocking GenerateContentResponse
for edge cases (similar to test_gemini_streamed_response_emits_text_events_for_non_empty_parts).
This ensures 100% code coverage for the file search tool implementation.

Author: gorkachea

tests/models/test_google.py

@@ -4113,6 +4113,102 @@ async def test_google_model_file_search_tool_stream(allow_model_requests: None,
             await client.aio.file_search_stores.delete(name=store.name, config={'force': True})
 
 
+async def test_google_model_file_search_empty_grounding_chunks():
+    """Test that file search handles empty grounding_chunks gracefully."""
+    # Create a response with grounding_metadata but empty grounding_chunks
+    response = GenerateContentResponse.model_validate(
+        {
+            'response_id': 'test-123',
+            'model_version': 'gemini-test',
+            'usage_metadata': GenerateContentResponseUsageMetadata(
+                prompt_token_count=0,
+                candidates_token_count=0,
+            ),
+            'candidates': [
+                {
+                    'finish_reason': GoogleFinishReason.STOP,
+                    'content': {
+                        'role': 'model',
+                        'parts': [{'text': 'Some text'}],
+                    },
+                    'grounding_metadata': {
+                        'grounding_chunks': [],  # Empty grounding_chunks
+                    },
+                }
+            ],
+        }
+    )
+
+    async def response_iterator() -> AsyncIterator[GenerateContentResponse]:
+        yield response
+
+    streamed_response = GeminiStreamedResponse(
+        model_request_parameters=ModelRequestParameters(),
+        _model_name='gemini-test',
+        _response=response_iterator(),
+        _timestamp=IsDatetime(),
+        _provider_name='test-provider',
+        _provider_url='',
+    )
+    # Set _file_search_tool_call_id to trigger the code path
+    streamed_response._file_search_tool_call_id = 'test-tool-call-id'  # pyright: ignore[reportPrivateUsage]
+
+    events = [event async for event in streamed_response._get_event_iterator()]  # pyright: ignore[reportPrivateUsage]
+    # Should not crash and should emit text event
+    assert len(events) > 0
+    assert any(isinstance(event.part, TextPart) if hasattr(event, 'part') else False for event in events)
+
+
+async def test_google_model_file_search_empty_retrieved_contexts():
+    """Test that file search handles empty retrieved_contexts gracefully."""
+    # Create a response with grounding_chunks but no retrieved_context
+    response = GenerateContentResponse.model_validate(
+        {
+            'response_id': 'test-123',
+            'model_version': 'gemini-test',
+            'usage_metadata': GenerateContentResponseUsageMetadata(
+                prompt_token_count=0,
+                candidates_token_count=0,
+            ),
+            'candidates': [
+                {
+                    'finish_reason': GoogleFinishReason.STOP,
+                    'content': {
+                        'role': 'model',
+                        'parts': [{'text': 'Some text'}],
+                    },
+                    'grounding_metadata': {
+                        'grounding_chunks': [
+                            {
+                                # Chunk without retrieved_context
+                            }
+                        ],
+                    },
+                }
+            ],
+        }
+    )
+
+    async def response_iterator() -> AsyncIterator[GenerateContentResponse]:
+        yield response
+
+    streamed_response = GeminiStreamedResponse(
+        model_request_parameters=ModelRequestParameters(),
+        _model_name='gemini-test',
+        _response=response_iterator(),
+        _timestamp=IsDatetime(),
+        _provider_name='test-provider',
+        _provider_url='',
+    )
+    # Set _file_search_tool_call_id to trigger the code path
+    streamed_response._file_search_tool_call_id = 'test-tool-call-id'  # pyright: ignore[reportPrivateUsage]
+
+    events = [event async for event in streamed_response._get_event_iterator()]  # pyright: ignore[reportPrivateUsage]
+    # Should not crash and should emit text event
+    assert len(events) > 0
+    assert any(isinstance(event.part, TextPart) if hasattr(event, 'part') else False for event in events)
+
+
 async def test_cache_point_filtering():
     """Test that CachePoint is filtered out in Google internal method."""
     from pydantic_ai import CachePoint