principle-test-behavior-not-implementation from theonlyfusioncube/potetos-for-everyone is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.
Call the system the way its consumer does and assert meaningful observable output; avoid mocks or assertions that only mirror internal calls. Use when when writing or evaluating tests.
Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.
What the file says
# Test Behavior, Not Implementation
## Trigger
When writing or evaluating tests.
## Rule
Call the system the way its consumer does and assert meaningful observable output; avoid mocks or assertions that only mirror internal calls.
## Application
1. Name the concrete decision this principle changes.
2. Apply the rule to that decision, not as a decorative citation.
3. Prefer evidence from the current repository/runtime over generic preference.
4. If the principle conflicts with an explicit user constraint, keep the constraint and state the tradeoff.
The line at the top of this page pins the label git:20260908.ec65ed5, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.
GET https://markdownregistry.com/api/v1/artifacts/art_olgw3u7lk2ownl2t
GET https://markdownregistry.com/api/v1/resolve?ref=theonlyfusioncube/potetos-for-everyone/principle-test-behavior-not-implementation
GET https://markdownregistry.com/api/v1/blob/b88e33c60a104c891b858c22504970731995ae5b0c42a1358a22d42f6a33e863
Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.
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