Apply when you write, change, or keep a test. Call the code as its users do and assert the exact result they see. Rewrite or delete a test that would pass if every imported function returned undefined.
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
A test calls the code as its users do and asserts the exact result they see. Rewrite or delete any test that would still pass if every imported function returned `undefined` or a wrong value.
These shapes fail that check:
- Loose or no assertion: `toBeDefined`, `toBeTruthy`, `not.toThrow`, `toBeGreaterThan(0)`.
- Call or absence only: `toHaveBeenCalled`, `not.toHaveBeenCalled`, `toBeUndefined`, `toEqual([])`.
- Expected value computed by the code under test: `expect(f(a)).toBe(f(a))`.
- Restated constant, config default, table row, or prompt string.
- Assertions on data the test built, with no call to the subject.
Fix: call the subject in the test body with one concrete input and assert the literal output or effect. For a mock, assert the payload it received. For an absence, also assert the presence on another input. For a constant, test the mechanism that reads it with one input instead of restating the value.
Keep relation checks across table rows (a key in two tables, a parent that exists) and `*.test-d.ts` type checks.
The line at the top of this page pins the label git:20261013.9e6954c, 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.
A 17 of 17 checks passed. Fixed automatic checks with no AI involved, so the same checks give the same answer every run.
pass: Frontmatter block present
pass: Frontmatter declares a name
pass: Frontmatter declares a description
pass: Size between 200 bytes and 200 KB (1386 bytes)
pass: No zero-width or bidi control characters
pass: No instruction hidden inside an HTML comment
pass: No link to an exfiltration or paste host
pass: No credential-shaped string
pass: No instruction to send local credentials anywhere
pass: No text hidden with inline styles
pass: No prompt-injection phrasing
pass: No curl or wget piped into a shell
pass: No recursive delete of root, home or parent
pass: No instruction to read or print local credentials
pass: No base64 blob over 200 characters
pass: No link to a raw IP address
pass: No script tag
Source
GitHub
nightly-labs/openbot · 5,267 stars · license a license file GitHub does not identify · pushed 2026-11-04 · branch main
API
GET https://markdownregistry.com/api/v1/artifacts/art_tkzvfbe4op5bbzaz
GET https://markdownregistry.com/api/v1/resolve?ref=nightly-labs/openbot/principle-test-behavior-not-implementation
GET https://markdownregistry.com/api/v1/blob/b2b73ba42920f9c3174ecdf808ec6e4591b3a9266ada9a05814f386004266d3a
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