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_planner_node.py

@@ -0,0 +1,89 @@
+# 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.
+
+from unittest.mock import Mock, patch
+
+from artemis.agents.planner.planner import PlannerNode
+from artemis.context import DevicePlatform, ArtemisContext
+import pytest
+
+
+class DummyState:
+    def __init__(
+        self,
+        initial_goal,
+        needs_replan=False,
+        operator_raw_data=None,
+        operator_replan_reason=None,
+    ):
+        self.initial_goal = initial_goal
+        self.needs_replan = needs_replan
+        self.operator_raw_data = operator_raw_data
+        self.operator_replan_reason = operator_replan_reason
+
+    async def asanitize_update(self, ctx, update, agent):
+        return update
+
+
+@pytest.fixture
+def mock_context():
+    ctx = Mock(spec=ArtemisContext)
+    ctx.device = Mock()
+    ctx.device.mobile_platform = DevicePlatform.ANDROID
+    ctx.adb_client = Mock()
+    ctx.ui_adb_client = Mock()
+    mock_screen_data = Mock()
+    mock_screen_data.base64 = "YmFzZTY0"
+    mock_screen_data.elements = []
+    mock_screen_data.width = 1080
+    mock_screen_data.height = 2400
+    ctx.ui_adb_client.get_screen_data.return_value = mock_screen_data
+    ctx.data_engine = None
+
+    return ctx
+
+
+@pytest.mark.asyncio
+async def test_planner_initial_plan(mock_context):
+    state = DummyState(
+        initial_goal="Test Goal",
+        operator_raw_data={"screenshot_b64": "dummy_base64_string"},
+    )
+    node = PlannerNode(mock_context)
+
+    mock_llm = Mock()
+    mock_response = Mock()
+    mock_response.content = "- [ ] Subgoal 1"
+    mock_response.tool_calls = []
+
+    async def mock_astream(*args, **kwargs):
+        yield mock_response
+
+    mock_llm.astream.side_effect = mock_astream
+    mock_llm.bind_tools = Mock(return_value=mock_llm)
+
+    with patch("artemis.agents.planner.planner.get_llm", return_value=mock_llm):
+        await node(state)
+
+        assert mock_llm.astream.called
+        args, kwargs = mock_llm.astream.call_args
+        messages = args[0]
+
+        system_msg = messages[0].content
+        assert "## Role" in system_msg
+
+        human_msg_content = messages[1].content
+        assert isinstance(human_msg_content, list)
+        assert human_msg_content[0]["type"] == "text"
+        assert "Goal: Test Goal" in human_msg_content[0]["text"]