diff --git a/CLAUDE.md b/CLAUDE.md
index ed69773..0ffc880 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -102,13 +102,19 @@ Each Nextcloud app has a corresponding server module that:
 - **Important**: Integration tests run against live Docker containers. After making code changes to the MCP server, rebuild only the MCP container with `docker-compose up --build -d mcp` before running tests
 
 #### Testing Best Practices
-- **Always restart MCP server** after code changes with `docker-compose up --build -d mcp`
+- **MANDATORY: Always run tests after implementing features or fixing bugs**
+  - Run tests to completion before considering any task complete
+  - If tests require modifications to pass, ask for permission before proceeding
+  - Use `docker-compose up --build -d mcp` to rebuild MCP container after code changes
 - **Use existing fixtures** from `tests/conftest.py` to avoid duplicate setup work:
   - `nc_mcp_client` - MCP client session for tool/resource testing  
   - `nc_client` - Direct NextcloudClient for setup/cleanup operations
   - `temporary_note` - Creates and cleans up test notes automatically
   - `temporary_addressbook` - Creates and cleans up test address books
   - `temporary_contact` - Creates and cleans up test contacts
+- **Test specific functionality** after changes:
+  - For Notes changes: `uv run pytest tests/integration/test_mcp.py -k "notes" -v`
+  - For specific API changes: `uv run pytest tests/integration/test_notes_api.py -v`
 - **Avoid creating standalone test scripts** - use pytest with proper fixtures instead
 
 ### Configuration Files
diff --git a/tests/integration/test_mcp.py b/tests/integration/test_mcp.py
index c748973..136afeb 100644
--- a/tests/integration/test_mcp.py
+++ b/tests/integration/test_mcp.py
@@ -334,10 +334,13 @@ async def test_mcp_notes_etag_conflict(
         )
 
         # 4. Verify the update was rejected with a 412 error
-        assert conflict_result.isError is True, "Update with stale ETag should fail"
-        error_content = conflict_result.content[0].text
-        assert "modified by someone else" in error_content or "412" in error_content, (
-            f"Expected conflict error message, got: {error_content}"
+        # The MCP framework doesn't set isError=True for ErrorResponse, so check the response content
+        response_content = conflict_result.content[0].text
+        response_data = json.loads(response_content)
+
+        assert response_data["success"] is False, "Update with stale ETag should fail"
+        assert "modified by someone else" in response_data["error"], (
+            f"Expected conflict error message, got: {response_data}"
         )
 
         logger.info("Successfully verified ETag conflict handling via MCP")