Agent Series (21): Harness Testing — 45 Tests, How They're Designed, and What Bu

<h2> From Demo Code to a Reusable Package </h2> <p>Article 19 used a 900-line <code>harness_full_demo.py</code> to demonstrate eight defense layers. That file is good for

<p>A patch touches zero test files. No assertion changes, no new skips, no fixture edits. The suite goes green on the first run.</p> <p>Then someone opens the job duration graph

<p>Your agent tests pass. Your monitoring says "green."</p> <p>Meanwhile, your agent just hallucinated a refund policy, leaked a customer's SSN, and burned $2,847 in a token

<h1> Day 21: The Quality Architect — The Complete Testing Ecosystem &amp; Pytest </h1> <p>14 min read<br /> Series: Logic &amp; Legacy<br /> Day 21 / 30<br /> Level: Senior