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Agent skill

Seam-Based TDD

by Yeachan-Heo in Yeachan-Heo/oh-my-claudecode

Test-first loop at pre-agreed seams: write one failing test, make it pass with the smallest change, repeat, with expected values taken from an independent source.

MITAuto-check passedTesting & QA

Install Seam-Based TDD

skills CLI
$ npx skills add Yeachan-Heo/oh-my-claudecode --skill tdd -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install Yeachan-Heo/oh-my-claudecode tdd --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/Yeachan-Heo/oh-my-claudecode.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/tdd .claude/skills/tdd && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
tdd
GitHub stars
40k
Token cost
~477 tokens
SKILL.md length
278 words
Files
1
Skills in repo
47
Repo updated
First seen
Licence
MIT

At a glance

Test-first loop at pre-agreed seams: write one failing test, make it pass with the smallest change, repeat, with expected values taken from an independent source.

  • Works in 3 steps: Write the next test at a seam. Run it.… → Implement the smallest change that turns… → Repeat. Each test is a tracer bullet: a…
  • Implementing a feature test-first at seams you have agreed on
  • SKILL.md covers The loop, Rules, When no seam fits and Output
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

The skill runs red-green in small steps at seams that were agreed in advance. In a launch run the seam list is the approved output of C2; otherwise you agree the seams with the agent before the first test exists, because a seam nobody approved gets no tests. Each cycle writes the next test, watches it fail for the expected reason, implements the smallest change that turns it green, then repeats, treating each test as a tracer bullet through the behavior.

Expected values must come from a spec line, worked example or documented output, never from the implementation. Substitutes are allowed only at the seam's declared boundary class: in-process, locally substitutable, owned-remote port or true-external. Refactoring is left to the review stage, and a bug fix starts with a failing test that reproduces it. When no approved seam fits, the agent stops and reports the missing seam as a finding. Output lists the seams used, the failing and passing runs and any seam-absence findings.

When your agent uses it

  • Implementing a feature test-first at seams you have agreed on
  • Fixing a bug by first writing a test that reproduces it
  • Checking that tests assert independent expectations rather than mirroring the code

Example prompts

  • “Agree the seams for the coupon module with me, then build it test-first.”
  • “Reproduce the duplicate-email bug in a failing test before changing any code.”
  • “Write the next failing test for the cart total and show the red run.”

Requirements

  • A project with a test runner the agent can execute

Workflow steps

3 steps, taken from the first numbered list in SKILL.md.

  1. Write the next test at a seam. Run it. Watch it fail for the reason you expect — a test that cannot fail is not a test.
  2. Implement the smallest change that turns it green.
  3. Repeat. Each test is a tracer bullet: a narrow but complete path through the behavior, not a layer finished in isolation.

What it can do on your machine

Read from SKILL.md and the folder at commit 454bae0. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md.

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Seam-Based TDD loads about 477 tokens when it runs. Until then it costs about 49 tokens; SKILL.md has 278 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~49
When it runs · the whole SKILL.md, loaded when a task matches
~477

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from Yeachan-Heo/oh-my-claudecode at commit 454bae0, republished under its MIT licence (© Yeachan-Heo). 278 words, ~477 tokens.

Download SKILL.mdSave it as .claude/skills/tdd/SKILL.md (or your agent's skills folder).
name
tdd
description
Test-first at pre-agreed seams — one test, one implementation, tracer-bullet red/green; independent expected values; substitutions only at the seam's boundary class; launch Phase 4 reference.

TDD

Red-green in small steps, at seams that were agreed in advance. In a launch run the seam list is C2's approved output; outside launch, agree the seams with the user before the first test exists — a seam nobody approved gets no tests.

The loop

One test → one implementation → repeat:

  1. Write the next test at a seam. Run it. Watch it fail for the reason you expect — a test that cannot fail is not a test.
  2. Implement the smallest change that turns it green.
  3. Repeat. Each test is a tracer bullet: a narrow but complete path through the behavior, not a layer finished in isolation.

Rules

  • Expected values come from an independent source of truth — a spec line, a worked example, a documented output. Never from the implementation under test: a test that asserts what the code happens to do is a mirror, not a check.
  • Substitute at the seam's declared boundary class only — in-process, locally substitutable, owned-remote port, or true-external, the class C2 records for each seam. No substitutes inside the boundary the test is exercising.
  • Refactoring is not part of the loop. It belongs to the review stage; the repair worker owns it. Do not refactor mid-red-green.
  • A bug fix starts with the failing test that reproduces it — reproduction before theory, the debugger's rule.

When no seam fits

If the behavior cannot be tested at any approved seam, stop and say so: report the missing seam as a finding (it feeds architecture-survey and refit) rather than inventing a seam or testing through internals.

Output

  • The seam list used, with boundary classes
  • Red/green evidence — the failing run and the passing run
  • Any seam-absence findings

© Yeachan-Heo, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in skills/tdd of Yeachan-Heo/oh-my-claudecode.

Open the folder on GitHubat commit 454bae0

Compare with similar skills

Seam-Based TDD next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Seam-Based TDD compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Seam-Based TDD this skillYeachan-Heo/oh-my-claudecode40k—~477Automated safety check: PassMIT
Golang Testingantoniopaya22/go-rest-template1729 repos~4.2kAutomated safety check: PassNone
Agent Harness Testing Methodologyhuiliyi37/Tianshu-harness1.1k—~1kAutomated safety check: NotesApache-2.0
Designing TestsCloudAI-X/opencode-workflow275—~2.9kAutomated safety check: PassMIT
Python Testingaffaan-m/ECC276k6 repos~4.7kAutomated safety check: PassMIT
Rust Testingkurealnum/dotfiles2906 repos~2.9kAutomated safety check: PassNone

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Categories

Questions about Seam-Based TDD

What does Seam-Based TDD do?

Test-first loop at pre-agreed seams: write one failing test, make it pass with the smallest change, repeat, with expected values taken from an independent source. The skill runs red-green in small steps at seams that were agreed in advance. In a launch run the seam list is the approved output of C2; otherwise you agree the seams with the agent before the first test exists, because a seam nobody approved gets no tests.

When should I use Seam-Based TDD?

Seam-Based TDD fits situations like: implementing a feature test-first at seams you have agreed on; fixing a bug by first writing a test that reproduces it; checking that tests assert independent expectations rather than mirroring the code.

How do I install Seam-Based TDD in Claude Code?

Run `npx skills add Yeachan-Heo/oh-my-claudecode --skill tdd -a claude-code`. Or copy the skill folder (skills/tdd in Yeachan-Heo/oh-my-claudecode) into .claude/skills/tdd in your project. Claude Code loads it when a task matches its description.

How do I install Seam-Based TDD in Codex?

Run `npx skills add Yeachan-Heo/oh-my-claudecode --skill tdd -a codex`. Or copy the skill folder (skills/tdd in Yeachan-Heo/oh-my-claudecode) into .agents/skills/tdd in your project. Codex loads it when a task matches its description.

Can I use Seam-Based TDD in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add Yeachan-Heo/oh-my-claudecode --skill tdd -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/tdd, .gemini/skills/tdd, .github/skills/tdd and .opencode/skills/tdd in your project.

What does Seam-Based TDD need to run?

SKILL.md names no scripts, command-line tools or credentials: Seam-Based TDD is instructions for the agent only. Our summary lists: A project with a test runner the agent can execute.

Does Seam-Based TDD access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Seam-Based TDD safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Seam-Based TDD use?

Seam-Based TDD is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Seam-Based TDD use?

About 477 tokens (SKILL.md is roughly 1.9k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Seam-Based TDD?

Skills that share tags, products or a category with Seam-Based TDD: Golang Testing (antoniopaya22/go-rest-template, 172 stars), Agent Harness Testing Methodology (huiliyi37/Tianshu-harness, 1.1k stars), Designing Tests (CloudAI-X/opencode-workflow, 275 stars) and Python Testing (affaan-m/ECC, 276k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Seam-Based TDD?

Yeachan-Heo (a GitHub user) maintains it in Yeachan-Heo/oh-my-claudecode, which has 39,751 GitHub stars. The repository holds 47 skills in this directory. The repository was last updated on October 8, 2026.

Source: Yeachan-Heo/oh-my-claudecode on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.