Minimum Requirements for a Custom Logger, with an Integration Test Checklist (archived 2026-09-01)

To make a custom app's diagnostic logs trustworthy, we lay out UTF-8 JSON Lines, the required fields, flush, rotation, and failure behavior, plus the integration test angles using real files and real threads. Archived version of https://comcomponent.com/en/blog/2026/04/02/001-custom-logger-minimum-requirements-and-integration-test-checklist/, as published on 2026-09-01. The live article is maintained and may change after this date. First published 2026-04-02.