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/tools/validator/test_validator_tools.py

@@ -0,0 +1,75 @@
+# 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 base64
+from pathlib import Path
+
+from artemis.agents.validator.failure_analyzer import ValidationErrorCategory
+from artemis.agents.validator.validator import ValidatorNode
+import pytest
+
+
+@pytest.mark.asyncio
+async def test_safety_net_validation(artemis_context, mock_state):
+    """Test the safety_net_validation tool."""
+    node = ValidatorNode(artemis_context)
+
+    action_item = {
+        "action": "tap",
+        "coordinates": [100, 200],
+        "target_text": "Submit",
+    }
+
+    # We pass session=None so it relies on fallback or fails gracefully
+    # We assert it runs without unhandled exceptions.
+    try:
+        passed, category, reason = await node._validate_action_precondition(
+            session=None, action_item=action_item, state=mock_state
+        )
+    except Exception as e:
+        pytest.fail(f"Tool raised an exception: {e}")
+
+    assert isinstance(passed, bool)
+    assert isinstance(category, ValidationErrorCategory)
+    assert isinstance(reason, str)
+
+
+@pytest.mark.asyncio
+async def test_safety_net_pixel_validation(artemis_context, mock_state):
+    """Test the safety_net_pixel_validation tool."""
+    node = ValidatorNode(artemis_context)
+
+    action_item = {"action": "tap", "coordinates": [100, 200]}
+
+    # Read the real screenshot from the mock_state to provide as pre_screenshot_b64
+    screenshot_path = mock_state.latest_screenshot
+    pre_screenshot_b64 = "dummy_base64"
+    if screenshot_path and Path(screenshot_path).exists():
+        with open(screenshot_path, "rb") as f:
+            pre_screenshot_b64 = base64.b64encode(f.read()).decode("utf-8")
+
+    try:
+        passed, category, reason = await node._validate_action_precondition_pixel(
+            session=None,
+            action_item=action_item,
+            pre_screenshot_b64=pre_screenshot_b64,
+            original_coords=[100, 200],
+            state=mock_state,
+        )
+    except Exception as e:
+        pytest.fail(f"Tool raised an exception: {e}")
+
+    assert isinstance(passed, bool)
+    assert isinstance(category, ValidationErrorCategory)
+    assert isinstance(reason, str)