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MasihMoafiMasihMoafi/skills/tdd/SKILL.md

tdd

Skill8 starsChanged 9 days agoMITView on GitHub

Test-driven development: the agent writes the failing test, then the code, one behavior at a time. Use when building a feature or fixing a bug test-first, or when the user says tdd, red-green, or test-first.

194 other projects use a version of this.

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The file

We split this skill into the rules it gives an agent

2 rules. 0 are common, 2 are distinctive, and 0 are very specific to this project.

  • 0

    Common

    Most of the 186 edited versions we read keep these.

  • 2

    Distinctive

    This author's own choices. Worth a look.

  • 0

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Distinctive:

    Write the failing test, then the code that passes it, one slice at a time.

    line 8
  2. Distinctive:

    Write the regression test first and show it failing on the current code for the intended reason.

    line 36

“Common” is measured: kept by at least 6 in 10 of the 186 edited versions of this file we could read. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

Test-driven development

Write the failing test, then the code that passes it, one slice at a time.

Before the first test

  1. Name the behavior in one line: input, expected outcome, non-goals.
  2. Pick the seam, the public boundary you test at (function, CLI, HTTP route, rendered UI).
  3. Find the repo's test command and run it once for the baseline.

The loop

  1. Red. One test for the next smallest behavior; run only it. It must fail because the behavior is missing; a typo, import or fixture failure is not red. If it passes at once, it is a characterization test: pick a behavior that is actually missing.
  2. Green. The smallest code that passes; rerun that test.
  3. Next slice. Let this slice shape the next test; never write them all up front.

Refactor once the behavior is complete and green, then rerun the relevant suite.

Code written before its test is deleted, not kept "as reference": a test written after passes at once and proves nothing. Exploring first is fine; throw the exploration away, then start at red. A test that is hard to write means an interface that is hard to use: simplify the interface.

A good test

  • Checks behavior through the seam and survives a refactor that keeps it.
  • Has one reason to fail; deterministic and fast.
  • Takes its expected value from an independent source. assert add(a, b) == a + b can never fail; assert add(2, 3) == 5 can.
  • Mocks only external boundaries (network, paid APIs, clock); makes no paid calls. A fake proves only the fake's boundary: say so.
  • For model and ML code, test the deterministic parts (transforms, parsing, shapes, prompt assembly, scoring math); model quality is an experiment.

Bugs

Write the regression test first and show it failing on the current code for the intended reason; a regression test that never failed proves nothing.

Done

Show the test command's red output before, the same command green after, and the wider suite green. Label the work honestly: TDD, regression test, characterization test or refactor.

Sources: mattpocock/skills (tdd); obra/superpowers (test-driven-development, MIT).

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