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/e2e/test_failure_analyzer_e2e_youtube.py

@@ -0,0 +1,124 @@
+# 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
+import logging
+import os
+import sys
+from unittest.mock import patch
+from dotenv import load_dotenv
+
+# Ensure we can import from project
+sys.path.append(os.path.dirname(__file__))
+
+from artemis.sdk import Agent
+from artemis.sdk.builders import Builders
+from artemis.sdk.types import AgentProfile
+from artemis.agents.validator.validator import ValidatorNode, ValidationErrorCategory
+
+logging.basicConfig(level=logging.INFO)
+logger = logging.getLogger("test_fa_e2e")
+
+# We want to fail the first validation to trigger the Failure Analyzer
+original_validate = ValidatorNode._validate_action_precondition
+original_validate_pixel = ValidatorNode._validate_action_precondition_pixel
+
+has_failed_once = False
+
+
+async def mock_validate_action_precondition(self, session, action_item, state=None):
+    global has_failed_once
+    if not has_failed_once:
+        has_failed_once = True
+        logger.warning(">>> MOCK VALIDATOR: Simulating pre-execution XML validation failure!")
+        return (
+            False,
+            ValidationErrorCategory.TARGET_DISAPPEARED,
+            "Simulated pre-execution XML validation failure",
+        )
+    return await original_validate(self, session, action_item, state=state)
+
+
+async def mock_validate_action_precondition_pixel(
+    self,
+    session,
+    action_item,
+    pre_screenshot_b64,
+    original_coords=None,
+    state=None,
+):
+    global has_failed_once
+    if not has_failed_once:
+        has_failed_once = True
+        logger.warning(">>> MOCK VALIDATOR: Simulating pre-execution Pixel validation failure!")
+        return (
+            False,
+            ValidationErrorCategory.TARGET_DISAPPEARED,
+            "Simulated pre-execution Pixel validation failure",
+        )
+    return await original_validate_pixel(
+        self,
+        session,
+        action_item,
+        pre_screenshot_b64,
+        original_coords,
+        state=state,
+    )
+
+
+async def main():
+    load_dotenv()
+
+    # Check if emulator/device is connected
+    import subprocess
+
+    res = subprocess.run(["adb", "devices"], capture_output=True, text=True)
+    print("ADB Devices:")
+    print(res.stdout)
+
+    # 1. Initialize agent
+    logger.info("Initializing Agent...")
+    profile = AgentProfile(name="default", from_file="llm-config.override.jsonc")
+    config = Builders.AgentConfig.with_default_profile(profile).build()
+
+    agent = Agent(config=config)
+    await agent.init()
+
+    # 2. Run the task with patches
+    goal = "Play a video in full screen on YouTube in Chrome"
+    logger.info(f"Running task with goal: {goal}")
+
+    with (
+        patch.object(
+            ValidatorNode,
+            "_validate_action_precondition",
+            mock_validate_action_precondition,
+        ),
+        patch.object(
+            ValidatorNode,
+            "_validate_action_precondition_pixel",
+            mock_validate_action_precondition_pixel,
+        ),
+    ):
+        try:
+            result = await agent.run_task(goal=goal, name="test_fa_youtube_fullscreen")
+            logger.info(f"Task finished! Result: {result}")
+        except Exception:
+            logger.exception("Error during execution:")
+        finally:
+            await agent.clean()
+
+
+if __name__ == "__main__":
+    asyncio.run(main())