//www.martinrichards.me/tags/refactoring/ Recent content in Refactoring on Martin C. Richards Hugo en Sun, 17 May 2026 08:39:41 +0200 //www.martinrichards.me/post/test_behaviour_not_implementation/ Sun, 17 May 2026 08:39:41 +0200 //www.martinrichards.me/post/test_behaviour_not_implementation/ <picture> <source type="image/webp" class="cover-image" srcset=" /img/frigate-schematics_hu_64cb0b87de23b583.webp 400w, /img/frigate-schematics_hu_8069a4136daf8728.webp 800w, /img/frigate-schematics_hu_389af5879e0c16cc.webp 1200w" sizes="(max-width: 720px) 100vw, 720px" loading="lazy" decoding="async" alt="Frigate Schematics"> <img class="cover-image" src="//www.martinrichards.me/img/frigate-schematics.png" loading="lazy" decoding="async" alt="Frigate Schematics"> </picture> <h1 id="test-behaviour-not-implementation">Test behaviour, not implementation</h1> <p>Most testing arguments get lost in theoretical minutiae and miss the point: validating correctness. Testing units at every level makes tests brittle and code resistant to change. Testing full vertical slices is too coarse - it&rsquo;s hard to cover invariants and edge cases.</p> <p>What you want is something in the middle. Validate the edges with real components - make real HTTP calls, send actual messages on the queue, run real queries against a real DB, check the domain gets invoked correctly. Then validate your domain at its interface: mock the edges, mock the unexpected behaviour, make sure the domain behaves as expected.</p>