test: add comprehensive unit, integration, and e2e test suites

Introduce complete test coverage for the ARTEMIS platform across multiple layers:
Unit tests: Add tests for agent nodes (Planner, Operator, Validator, Diagnoser, FlashRunner, Explorer), tools, utils (OCR/XML fusion, UI hierarchy), and data engine.
Integration tests: Add live tool verification, reactive runner, IME, and standalone workflow tests.
E2E tests: Add end-to-end scenario tests for media playback and failure recovery flows.
Fixtures & mocks: Add mock inputs (audio, video, screenshot) and test utilities.

tests/unit/agents/test_snapshot_rollback.py

@@ -0,0 +1,112 @@
+# 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 asyncio
+from unittest.mock import AsyncMock, MagicMock, patch
+
+from artemis.agents.operator.operator import OperatorNode
+from artemis.context import ArtemisContext
+from artemis.graph.graph import execution_check_node
+from artemis.graph.state import State
+import pytest
+
+
+@pytest.mark.asyncio
+async def test_snapshot_rollback_flow(tmp_path):
+    # Setup dummy directories
+    base_dir = tmp_path / "trace"
+    notes_dir = base_dir / "notes"
+    notes_dir.mkdir(parents=True)
+
+    task_plan_path = notes_dir / "task_plan.md"
+    task_plan_path.write_text("Initial Plan", encoding="utf-8")
+
+    # Mock Context
+    mock_ctx = MagicMock(spec=ArtemisContext)
+    mock_ctx.data_engine = MagicMock()
+    mock_ctx.data_engine.base_dir = base_dir
+    mock_ctx.execution_setup = None
+
+    # Mock State
+    mock_state = MagicMock(spec=State)
+    mock_state.subagent_calls = []
+    mock_state.asanitize_update = AsyncMock(return_value={"status": "success"})
+    mock_state.initial_goal = "Test goal"
+    mock_state.short_term_memory = ""
+    mock_state.operator_raw_data = {
+        "screenshot_b64": "YmFzZTY0",
+        "xml_hierarchy": "<hierarchy></hierarchy>",
+        "ocr_results": [],
+    }
+    mock_state.current_step_id = "test-step-id"
+
+    # Mock Controller and LLM to let Operator run minimally
+    mock_controller = MagicMock()
+    mock_controller.take_screenshot = AsyncMock(return_value="YmFzZTY0")
+    mock_device_data = MagicMock()
+    mock_device_data.elements = []
+    mock_controller.get_screen_data = AsyncMock(return_value=mock_device_data)
+
+    mock_llm = MagicMock()
+    mock_response = MagicMock()
+    mock_response.tool_calls = []
+
+    async def mock_astream(*args, **kwargs):
+        yield mock_response
+
+    mock_llm.astream.side_effect = mock_astream
+    mock_llm.bind_tools.return_value = mock_llm
+
+    # 1. Run Operator to trigger snapshot
+    with patch("artemis.agents.operator.operator.get_llm", return_value=mock_llm):
+        node = OperatorNode(mock_ctx)
+        await node(mock_state)
+
+    # Verify snapshot was created
+    snapshot_dir = notes_dir.with_name("notes_snapshot")
+    assert snapshot_dir.exists()
+    assert (snapshot_dir / "task_plan.md").read_text(encoding="utf-8") == "Initial Plan"
+    assert mock_ctx.task_plan_snapshot == snapshot_dir
+
+    # 2. Simulate Operator optimistic modification
+    task_plan_path.write_text("Modified Plan", encoding="utf-8")
+
+    # 3. Run execution_check_node with failure to trigger rollback
+    future = asyncio.Future()
+    future.set_result({"status": "failed"})
+    mock_ctx.checker_task = future
+
+    await execution_check_node(mock_state, mock_ctx)
+
+    # Verify rollback restored the file
+    assert task_plan_path.read_text(encoding="utf-8") == "Initial Plan"
+
+    # 4. Run Operator again to create new snapshot (simulate next attempt)
+    # First modify it again to simulate operator working on restored plan
+    task_plan_path.write_text("Modified Plan 2", encoding="utf-8")
+
+    with patch("artemis.agents.operator.operator.get_llm", return_value=mock_llm):
+        await node(mock_state)
+
+    assert (snapshot_dir / "task_plan.md").read_text(encoding="utf-8") == "Modified Plan 2"
+
+    # 5. Run execution_check_node with success to trigger commit (cleanup)
+    future_success = asyncio.Future()
+    future_success.set_result({"status": "success"})
+    mock_ctx.checker_task = future_success
+
+    await execution_check_node(mock_state, mock_ctx)
+
+    # Verify snapshot was deleted
+    assert not snapshot_dir.exists()