testing-principles

A set of general testing guidelines covering test-driven development, test quality, coverage, and test design. Test-driven development means writing a failing test, making it pass with the smallest change, then improving the code.

In plain words
What is it for?
Use it when writing tests, planning test coverage, reviewing test quality, or fixing reproducible bugs.
Why use it?
It keeps tests focused on meaningful behaviour instead of chasing coverage numbers or creating fragile, low-value tests.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/shinpr/claude-code-workflows/testing-principles
Any agent
npx skills add shinpr/claude-code-workflows --skill testing-principles
Clone the repo
git clone --depth 1 https://github.com/shinpr/claude-code-workflows

Made for: Claude Code, Codex.

Per session 40 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 811 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00040 $0.00811
Opus 5 $0.00020 $0.00405
Sonnet 5 $0.00008 $0.00162
Haiku 4.5 $0.00004 $0.00081

Measured 2d ago against content hash 3da24a71e449, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

testing-principles scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

dev-skills/skills/testing-principles/SKILL.md · 58 lines

How it starts

The opening of the file, as written. The whole thing — 58 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Language-Agnostic Testing Principles

Test-Driven Development (TDD)

Use this cycle for new or changed executable behavior and reproducible bug fixes. For a behavior-preserving refactor, first confirm existing tests pass or add passing characterization tests, then refactor and rerun the same regression evidence.

RED: confirm the new test fails for the intended reason. GREEN: implement the smallest passing change. REFACTOR: improve structure while the test remains green. VERIFY: run the repository's applicable regression checks.

Quality Requirements

  • Treat coverage as a diagnostic signal for finding untested areas, not a target — a target gets gamed into trivial tests (Goodhart's Law)
  • Concentrate tests on critical paths, business logic, and behavior whose regression would matter
  • Prioritize meaningful assertions over the coverage number; any CI threshold is the project's config, not a quality goal in itself
  • Use project-configured speed budgets when present. Otherwise investigate test speed only when observed feedback or CI cost is material to the current outcome; retain slower tests when their proof boundary requires it

Test Design Rules

  • Structure each test as Arrange, one Act, and Assert; multiple assertions may prove one behavior.
  • Follow the repository's test naming convention and name the condition and observable outcome.
  • Exercise behavior through a public or integration boundary. Assertions verify return values, outputs, errors, or state changes rather than private implementation.
  • Use independently derived literal, property, approved snapshot, or fixture expectations. An implementation-derived oracle cannot detect the same implementation defect.
  • Keep each test's expected outcome unconditional. Table-driven or property-based cases are acceptable when each case is reported distinctly and uses an independent oracle.
  • Cover accepted boundary and error behavior; derive cases from the contract instead of adding generic edge-case permutations.
  • Each test creates and cleans up its own state, passes in isolation and any order, and controls time or randomness that affects its result.
  • Keep tests executable. Fix or remove tests that no longer describe accepted behavior; restore tests disabled only to bypass a failure.

Read the full file on GitHub · 58 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 58 lines · 40 tokens per session scan A 3da24a71e449

Subscribe to this mod's changes

testing-principles is a skill published in the GitHub repository shinpr/claude-code-workflows (675 stars, last pushed 4d ago), licensed MIT. It adds 40 tokens to every session and 811 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Related

Other skills, from other repositories