feat: support pre-populated session events in SessionInput for eval cases

src/google/adk/evaluation/eval_case.py

@@ -23,6 +23,7 @@
 from pydantic import model_validator
 from typing_extensions import TypeAlias
 
+from ..events.event import Event
 from .app_details import AppDetails
 from .common import EvalBaseModel
 from .conversation_scenarios import ConversationScenario
@@ -124,6 +125,14 @@ class SessionInput(EvalBaseModel):
   state: SessionState = Field(default_factory=dict)
   """The state of the session."""
 
+  conversation_history: Optional[list[Event]] = None
+  """Optional list of events to seed the session with prior conversation history.
+
+  When provided, these events are appended to the session after creation but
+  before inference begins. This enables eval cases to test agent behavior that
+  depends on prior context without scoring the context turns.
+  """
+
 
 StaticConversation: TypeAlias = list[Invocation]
 """A conversation where the user's queries for each invocation are already specified."""

src/google/adk/evaluation/evaluation_generator.py

@@ -212,13 +212,19 @@ async def _generate_inferences_from_root_agent(
     user_id = initial_session.user_id if initial_session else "test_user_id"
     session_id = session_id if session_id else str(uuid.uuid4())
 
-    _ = await session_service.create_session(
+    session = await session_service.create_session(
         app_name=app_name,
         user_id=user_id,
         state=initial_session.state if initial_session else {},
         session_id=session_id,
     )
 
+    # Seed session with prior conversation history so that eval turns
+    # run with realistic prior context without being scored.
+    if initial_session and initial_session.conversation_history:
+      for event in initial_session.conversation_history:
+        await session_service.append_event(session=session, event=event)
+
     if not artifact_service:
       artifact_service = InMemoryArtifactService()
 

tests/unittests/evaluation/test_evaluation_generator.py

@@ -457,3 +457,112 @@ async def mock_generate_inferences_side_effect(
     mock_generate_inferences.assert_called_once()
     called_with_content = mock_generate_inferences.call_args.args[3]
     assert called_with_content.parts[0].text == "message 1"
+
+  @pytest.mark.asyncio
+  async def test_seed_events_are_appended_to_session(self, mocker, mock_runner):
+    """Tests that seed events from SessionInput.conversation_history are appended after create_session."""
+    from google.adk.evaluation.eval_case import SessionInput
+
+    mock_agent = mocker.MagicMock()
+    mock_user_sim = mocker.MagicMock(spec=UserSimulator)
+    mock_user_sim.get_next_user_message = mocker.AsyncMock(
+        return_value=NextUserMessage(
+            status=UserSimulatorStatus.STOP_SIGNAL_DETECTED
+        )
+    )
+
+    # Create a real InMemorySessionService so we can verify events are appended
+    mock_session_service = mocker.MagicMock()
+    mock_session = mocker.MagicMock()
+    mock_session_service.create_session = mocker.AsyncMock(
+        return_value=mock_session
+    )
+    mock_session_service.append_event = mocker.AsyncMock()
+
+    mocker.patch(
+        "google.adk.evaluation.evaluation_generator.EvaluationGenerator._get_app_details_by_invocation_id"
+    )
+    mocker.patch(
+        "google.adk.evaluation.evaluation_generator.EvaluationGenerator.convert_events_to_eval_invocations"
+    )
+
+    seed_event_1 = Event(
+        content=types.Content(
+            parts=[types.Part(text="How do I pay my water bill?")],
+            role="user",
+        ),
+        author="user",
+        invocation_id="seed-0",
+    )
+    seed_event_2 = Event(
+        content=types.Content(
+            parts=[types.Part(text="You can pay by calling ABC.")],
+            role="model",
+        ),
+        author="root_agent",
+        invocation_id="seed-0",
+    )
+
+    initial_session = SessionInput(
+        app_name="test_app",
+        user_id="test_user",
+        conversation_history=[seed_event_1, seed_event_2],
+    )
+
+    await EvaluationGenerator._generate_inferences_from_root_agent(
+        root_agent=mock_agent,
+        user_simulator=mock_user_sim,
+        initial_session=initial_session,
+        session_service=mock_session_service,
+    )
+
+    # Verify append_event was called for each seed event
+    assert mock_session_service.append_event.call_count == 2
+    mock_session_service.append_event.assert_any_call(
+        session=mock_session, event=seed_event_1
+    )
+    mock_session_service.append_event.assert_any_call(
+        session=mock_session, event=seed_event_2
+    )
+
+  @pytest.mark.asyncio
+  async def test_no_seed_events_when_events_is_none(self, mocker, mock_runner):
+    """Tests that append_event is not called when SessionInput.conversation_history is None."""
+    from google.adk.evaluation.eval_case import SessionInput
+
+    mock_agent = mocker.MagicMock()
+    mock_user_sim = mocker.MagicMock(spec=UserSimulator)
+    mock_user_sim.get_next_user_message = mocker.AsyncMock(
+        return_value=NextUserMessage(
+            status=UserSimulatorStatus.STOP_SIGNAL_DETECTED
+        )
+    )
+
+    mock_session_service = mocker.MagicMock()
+    mock_session = mocker.MagicMock()
+    mock_session_service.create_session = mocker.AsyncMock(
+        return_value=mock_session
+    )
+    mock_session_service.append_event = mocker.AsyncMock()
+
+    mocker.patch(
+        "google.adk.evaluation.evaluation_generator.EvaluationGenerator._get_app_details_by_invocation_id"
+    )
+    mocker.patch(
+        "google.adk.evaluation.evaluation_generator.EvaluationGenerator.convert_events_to_eval_invocations"
+    )
+
+    initial_session = SessionInput(
+        app_name="test_app",
+        user_id="test_user",
+    )
+
+    await EvaluationGenerator._generate_inferences_from_root_agent(
+        root_agent=mock_agent,
+        user_simulator=mock_user_sim,
+        initial_session=initial_session,
+        session_service=mock_session_service,
+    )
+
+    # Verify append_event was NOT called
+    mock_session_service.append_event.assert_not_called()