Test-driven development discipline: the red-green-refactor cycle, the testing pyramid's proportion of unit/integration/e2e, Fowler's test-double taxonomy, and the FIRST properties of a test worth keeping. Use when building a feature or fixing a bug test-first, mentions "TDD" or "red-green-refactor", or when deciding what kind of test to write, whether to mock a dependency, or how a test suite should be shaped.
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# Test-Driven Development
TDD is a design discipline, not a testing habit. Kent Beck's rule is absolute: **no production code is written except to make a failing test pass, and no more of it than the test requires.** The test comes first because it forces the interface to be designed from the caller's side before an implementation exists to bias the design.
## Phase 1: The cycle
One cycle, repeated, never skipped:
1. **Red.** Write the smallest test that expresses one new piece of behaviour, for code that does not yet support it. Run it. Confirm it fails, and fails for the reason you expect; a test that fails on a typo or a missing import isn't red for the right reason.
2. **Green.** Write the minimum production code that makes the test pass. Resist the urge to generalize or handle a case the test didn't ask for; a case not yet demanded by a test is a case not yet designed, and designing it now is a guess.
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Source
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aethrox/doctrine · 19 stars · license MIT · pushed 2026-09-11 · branch main
API
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aethrox/doctrine · skills/code-style-lint/SKILL.md · Discipline for code style and static analysis, adopt the ecosystem's established formatter as the non-negotiable source…
aethrox/doctrine · skills/codebase-design/SKILL.md · Module design discipline from John Ousterhout's A Philosophy of Software Design, depth as the metric (a lot of…
aethrox/doctrine · skills/dependency-upgrade-management/SKILL.md · Discipline for keeping dependencies current and deprecating capabilities safely, an inventory (SBOM) of what's actually…
aethrox/doctrine · skills/diagnosing-bugs/SKILL.md · Systematic debugging discipline based on David Agans' nine rules, understand the system, reproduce reliably, bisect the…
aethrox/doctrine · skills/domain-modeling/SKILL.md · Domain-Driven Design discipline, build a ubiquitous language shared by code and conversation, draw explicit bounded…
aethrox/doctrine · skills/explain-plainly/SKILL.md · Default to explaining technical work in plain language for a non-technical audience, using an existing project glossary…
aethrox/doctrine · skills/grilling/SKILL.md · Interview the user relentlessly, in rounds, to close the gap between what's known and what's needed before acting on a…
aethrox/doctrine · skills/handoff/SKILL.md · Hand off in-progress work, an on-call shift, or an open incident to another person or agent using a fixed four-part…
cursor/plugins · pstack/skills/tdd/SKILL.md · Use only when the user explicitly asks for TDD, a failing test, or a regression test, OR when the bug has an obvious…
cursor/plugins · harness/pstack/claude-code/skills/tdd/SKILL.md · Use only when the user explicitly asks for TDD, a failing test, or a regression test, OR when the bug has an obvious…
nightly-labs/openbot · marketplace/production-catalog/bundles/pstack/skills/tdd/SKILL.md · Use only when the user explicitly asks for TDD, a failing test, or a regression test, OR when the bug has an obvious…
michael-denyer/pstack-claude · plugins/pstack/skills/tdd/SKILL.md · Use only when the user explicitly asks for TDD, a failing test, or a regression test, OR when the bug has an obvious…
backnotprop/pstack · skills/tdd/SKILL.md · Use only when the user explicitly asks for TDD, a failing test, or a regression test, OR when the bug has an obvious…
