fix: Save output in state via output_key only when the event is authored by current agent

src/google/adk/agents/llm_agent.py

@@ -431,12 +431,22 @@ def _llm_flow(self) -> BaseLlmFlow:
 
   def __maybe_save_output_to_state(self, event: Event):
     """Saves the model output to state if needed."""
+    # skip if the event was authored by some other agent (e.g. current agent
+    # transferred to another agent)
+    if event.author != self.name:
+      logger.debug(
+          'Skipping output save for agent %s: event authored by %s',
+          self.name,
+          event.author,
+      )
+      return
     if (
         self.output_key
         and event.is_final_response()
         and event.content
         and event.content.parts
     ):
+
       result = ''.join(
           [part.text if part.text else '' for part in event.content.parts]
       )

tests/unittests/agents/test_llm_agent_output_save.py

@@ -0,0 +1,210 @@
+# Copyright 2025 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.
+
+"""Unit tests for LlmAgent output saving functionality."""
+
+from unittest.mock import Mock
+from unittest.mock import patch
+
+from google.adk.agents.llm_agent import LlmAgent
+from google.adk.events.event import Event
+from google.adk.events.event_actions import EventActions
+from google.genai import types
+from pydantic import BaseModel
+import pytest
+
+
+class MockOutputSchema(BaseModel):
+  message: str
+  confidence: float
+
+
+def create_test_event(
+    author: str = "test_agent",
+    content_text: str = "Hello world",
+    is_final: bool = True,
+    invocation_id: str = "test_invocation",
+) -> Event:
+  """Helper to create test events."""
+  # Create mock content
+  parts = [types.Part.from_text(text=content_text)] if content_text else []
+  content = types.Content(role="model", parts=parts) if parts else None
+
+  # Create event
+  event = Event(
+      invocation_id=invocation_id,
+      author=author,
+      content=content,
+      actions=EventActions(),
+  )
+
+  # Mock is_final_response if needed
+  if not is_final:
+    event.partial = True
+
+  return event
+
+
+class TestLlmAgentOutputSave:
+  """Test suite for LlmAgent output saving functionality."""
+
+  def test_maybe_save_output_to_state_skips_different_author(self, caplog):
+    """Test that output is not saved when event author differs from agent name."""
+    agent = LlmAgent(name="agent_a", output_key="result")
+    event = create_test_event(author="agent_b", content_text="Response from B")
+
+    with caplog.at_level("DEBUG"):
+      agent._LlmAgent__maybe_save_output_to_state(event)
+
+    # Should not add anything to state_delta
+    assert len(event.actions.state_delta) == 0
+
+    # Should log the skip
+    assert (
+        "Skipping output save for agent agent_a: event authored by agent_b"
+        in caplog.text
+    )
+
+  def test_maybe_save_output_to_state_saves_same_author(self):
+    """Test that output is saved when event author matches agent name."""
+    agent = LlmAgent(name="test_agent", output_key="result")
+    event = create_test_event(author="test_agent", content_text="Test response")
+
+    agent._LlmAgent__maybe_save_output_to_state(event)
+
+    # Should save to state_delta
+    assert event.actions.state_delta["result"] == "Test response"
+
+  def test_maybe_save_output_to_state_no_output_key(self):
+    """Test that nothing is saved when output_key is not set."""
+    agent = LlmAgent(name="test_agent")  # No output_key
+    event = create_test_event(author="test_agent", content_text="Test response")
+
+    agent._LlmAgent__maybe_save_output_to_state(event)
+
+    # Should not save anything
+    assert len(event.actions.state_delta) == 0
+
+  def test_maybe_save_output_to_state_not_final_response(self):
+    """Test that output is not saved for non-final responses."""
+    agent = LlmAgent(name="test_agent", output_key="result")
+    event = create_test_event(
+        author="test_agent", content_text="Partial response", is_final=False
+    )
+
+    agent._LlmAgent__maybe_save_output_to_state(event)
+
+    # Should not save partial responses
+    assert len(event.actions.state_delta) == 0
+
+  def test_maybe_save_output_to_state_no_content(self):
+    """Test that nothing is saved when event has no content."""
+    agent = LlmAgent(name="test_agent", output_key="result")
+    event = create_test_event(author="test_agent", content_text="")
+
+    agent._LlmAgent__maybe_save_output_to_state(event)
+
+    # Should not save empty content
+    assert len(event.actions.state_delta) == 0
+
+  def test_maybe_save_output_to_state_with_output_schema(self):
+    """Test that output is processed with schema when output_schema is set."""
+    agent = LlmAgent(
+        name="test_agent", output_key="result", output_schema=MockOutputSchema
+    )
+
+    # Create event with JSON content
+    json_content = '{"message": "Hello", "confidence": 0.95}'
+    event = create_test_event(author="test_agent", content_text=json_content)
+
+    agent._LlmAgent__maybe_save_output_to_state(event)
+
+    # Should save parsed and validated output
+    expected_output = {"message": "Hello", "confidence": 0.95}
+    assert event.actions.state_delta["result"] == expected_output
+
+  def test_maybe_save_output_to_state_multiple_parts(self):
+    """Test that multiple text parts are concatenated."""
+    agent = LlmAgent(name="test_agent", output_key="result")
+
+    # Create event with multiple text parts
+    parts = [
+        types.Part.from_text(text="Hello "),
+        types.Part.from_text(text="world"),
+        types.Part.from_text(text="!"),
+    ]
+    content = types.Content(role="model", parts=parts)
+
+    event = Event(
+        invocation_id="test_invocation",
+        author="test_agent",
+        content=content,
+        actions=EventActions(),
+    )
+
+    agent._LlmAgent__maybe_save_output_to_state(event)
+
+    # Should concatenate all text parts
+    assert event.actions.state_delta["result"] == "Hello world!"
+
+  def test_maybe_save_output_to_state_agent_transfer_scenario(self, caplog):
+    """Test realistic agent transfer scenario."""
+    # Scenario: Agent A transfers to Agent B, Agent B produces output
+    # Agent A should not save Agent B's output
+
+    agent_a = LlmAgent(name="support_agent", output_key="support_result")
+    agent_b_event = create_test_event(
+        author="billing_agent", content_text="Your bill is $100"
+    )
+
+    with caplog.at_level("DEBUG"):
+      agent_a._LlmAgent__maybe_save_output_to_state(agent_b_event)
+
+    # Agent A should not save Agent B's output
+    assert len(agent_b_event.actions.state_delta) == 0
+    assert (
+        "Skipping output save for agent support_agent: event authored by"
+        " billing_agent"
+        in caplog.text
+    )
+
+  def test_maybe_save_output_to_state_case_sensitive_names(self, caplog):
+    """Test that agent name comparison is case-sensitive."""
+    agent = LlmAgent(name="TestAgent", output_key="result")
+    event = create_test_event(author="testagent", content_text="Test response")
+
+    with caplog.at_level("DEBUG"):
+      agent._LlmAgent__maybe_save_output_to_state(event)
+
+    # Should not save due to case mismatch
+    assert len(event.actions.state_delta) == 0
+    assert (
+        "Skipping output save for agent TestAgent: event authored by testagent"
+        in caplog.text
+    )
+
+  @patch("google.adk.agents.llm_agent.logger")
+  def test_maybe_save_output_to_state_logging(self, mock_logger):
+    """Test that debug logging works correctly."""
+    agent = LlmAgent(name="agent1", output_key="result")
+    event = create_test_event(author="agent2", content_text="Test response")
+
+    agent._LlmAgent__maybe_save_output_to_state(event)
+
+    # Should call logger.debug with correct parameters
+    mock_logger.debug.assert_called_once_with(
+        "Skipping output save for agent %s: event authored by %s",
+        "agent1",
+        "agent2",
+    )