New: 98,000+ skills indexed from GitHub repos with 100+ stars · every skill safety-checkedBrowse top skillsTop skills
Esc to closeBrowse all skills
Submit a skillBrowse skills
Submit a skillBrowse skills

Official agent skill

Writing Tests

by PostHog in PostHog/posthog

Gates whether a new test should exist and forces it to be efficient, protecting CI from low-value test bloat.

OfficialCustom licenceAuto-check passedTesting & QA

Install Writing Tests

skills CLI
$ npx skills add PostHog/posthog --skill writing-tests -a claude-code

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

GitHub CLI
$ gh skill install PostHog/posthog writing-tests --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/PostHog/posthog.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/writing-tests .claude/skills/writing-tests && 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
writing-tests
GitHub stars
40k
Token cost
~5.9k tokens
SKILL.md length
3,272 words
Files
3 (incl. references)
Skills in repo
252
Repo updated
First seen
Licence
Custom licence

At a glance

Gates whether a new test should exist and forces it to be efficient, protecting CI from low-value test bloat.

  • Works in 2 steps: Does it earn its place? → Where does it go?
  • Tasks that involve Unit testing
  • SKILL.md covers The gate: two questions, Don't write it — the five no's, If you write it — weight it… and Before you open the PR, plus 1 more section
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Writing Tests is an agent skill from PostHog/posthog, published by the product's own GitHub organization. Gates whether a new test should exist and forces it to be efficient, protecting CI from low-value test bloat. Use before any change to what a pytest, Jest, or Playwright test asserts or sets up, down to one fixture or one assertion added to an existing block. Front-loads the value bar (every test must catch a realistic regression no existing test already catches; extend the nearest existing test before writing a new standalone one; test behavior through the public interface, not implementation details; collapse…

Its SKILL.md is about 5.9k tokens, which your agent loads only when the skill is triggered. The skill folder holds 3 other files, including reference files (for example `references/database-free-test-classes.md` and `references/mistakes-we-make.md`).

It sits in Testing & QA, covering Unit testing, Failing and flaky tests and Backend development. It works with Playwright, pytest, Django and Jest. The repository describes itself as: :hedgehog: PostHog is the leading platform for building self-driving products. Our developer tools – AI observability, analytics, session replay, flags, experiments, error…

When your agent uses it

  • Tasks that involve Unit testing
  • Tasks that involve Failing and flaky tests
  • Tasks that involve Backend development

Example prompts

  • “t write it”
  • “Use the writing-tests skill to gate whether a new test should exist and forces it to be efficient, protecting CI from low-value test bloat”
  • “/writing-tests”

Requirements

  • Python 3

Workflow steps

2 steps, taken from the step headings in SKILL.md.

  1. Does it earn its place?
  2. Where does it go?

What it can do on your machine

Read from SKILL.md and the folder at commit 10f9ad7. 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 (its code samples are python).

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

  • Network

    Links to these hosts (documentation or services it may open):

    • testing.googleblog.com
    • posthog.com

    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

Writing Tests loads about 5.9k tokens when it runs, and up to ~9.5k if it reads all its reference files. Until then it costs about 256 tokens; SKILL.md has 3,272 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~256
When it runs · the whole SKILL.md, loaded when a task matches
~5.9k
With references · SKILL.md plus every file in references/, read only if the agent opens them
~9.5k

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

Its licence (Custom licence) doesn't allow us to republish the file, so here is its outline and opening line. It has 3,272 words (~5,917 tokens).

“The rationale and the same rules in human-facing form live in the handbook: Backend coding conventions › Testing (docs/published/handbook/engineering/conventions/backend-coding.md). This skill is the operational gate — run it before writing tests. It carries the decision procedure plus a catalog of…”

— opening of SKILL.md by PostHog, Custom licence
name
writing-tests

Read the full SKILL.md on GitHub

Files

SKILL.md and 2 other files (references) in .agents/skills/writing-tests of PostHog/posthog.

  • SKILL.md
  • references/database-free-test-classes.md
  • references/mistakes-we-make.md

Open the folder on GitHubat commit 10f9ad7

Used in 1 other repository

We found 1 copy of this SKILL.md (exact, near-identical or edited) in other folders. This page covers the copy in PostHog/posthog, which our catalogue first saw on October 7, 2026.

Compare with similar skills

Writing Tests 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.

Writing Tests compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Writing Tests this skillPostHog/posthog40k—~5.9kAutomated safety check: PassCustom licence
Designing TestsCloudAI-X/claude-workflow-v21.4k1 repos~1.5kAutomated safety check: PassMIT
Playwright Testingchongdashu/vibejam-starter-pack149—~2.1kAutomated safety check: PassNone
Playwright Testingchongdashu/vibejam-starter-pack149—~2.2kAutomated safety check: PassNone
Pytestmathiasertl/django-ca158—~924Automated safety check: PassGPL-3.0
Testingradix-ng/primitives274—~3.3kAutomated safety check: PassMIT

Similar skills

  • Designing Tests

    CloudAI-X/claude-workflow-v2

    Designs and implements testing strategies for any codebase. An agent skill from CloudAI-X/claude-workflow-v2.

    1.4k GitHub starsUsed in 1 repo~1.5k tokens
    Testing & QAAuto-check passed

  • Playwright Testing

    chongdashu/vibejam-starter-pack

    Plan, implement, and debug frontend tests: unit/integration/E2E/visual/a11y.

    149 GitHub stars~2.1k tokensUpdated 5 mo ago
    Testing & QAAuto-check passed

  • Playwright Testing

    chongdashu/vibejam-starter-pack

    Plan, implement, and debug frontend tests: unit/integration/E2E/visual/a11y.

    149 GitHub stars~2.2k tokensUpdated 5 mo ago
    Testing & QAAuto-check passed

  • Pytest

    mathiasertl/django-ca

    Instructions for running, writing, and maintaining tests in this project

    158 GitHub stars~924 tokensUpdated 4 days ago
    Testing & QAAuto-check passed

  • Testing

    radix-ng/primitives

    Test Radix NG primitives across every layer and pick the RIGHT one for a change: Vitest unit (zoneless), jest-axe a11y, Playwright browser regression (apps/visual-regression), SSR…

    274 GitHub stars~3.3k tokensUpdated 10 days ago
    Testing & QAAuto-check passed

  • Django TDD

    affaan-m/ECC

    Django testing strategies with pytest-django, TDD methodology, factoryboy, mocking, coverage, and testing Django REST Framework APIs.

    275k GitHub starsUsed in 7 repos~5.3k tokens
    Testing & QAAuto-check passed

More from PostHog/posthog

All 252 skills in this repo

  • Authoring Log Alerts

    PostHog/posthog

    Official

    Author useful, low-noise log alerts on services in a PostHog project.

    40k GitHub stars~3k tokensUpdated today
    Auto-check passed

  • Autoresolving PR Conflicts

    PostHog/posthog

    Official

    Operating procedure for the conflict-autoresolver agent: sweep open PostHog/posthog PRs that conflict with master, resolve the trivial conflicts (generated artifacts deterministically, source…

    40k GitHub stars~4.2k tokensUpdated today
    Auto-check passed

  • Diagnosing Stacktrace Symbolication

    PostHog/posthog

    Official

    Help users debug PostHog Error Tracking stack-trace symbolication for any supported platform — JavaScript/TypeScript web, React Native (Hermes), Android (Proguard / R8), or iOS / macOS (dSYM).

    40k GitHub stars~2.2k tokensUpdated today
    Auto-check passed

  • Exploring Apm Traces

    PostHog/posthog

    Official

    Investigates distributed application performance using PostHog APM (OpenTelemetry span) data via MCP.

    40k GitHub stars~3.5k tokensUpdated today
    Auto-check passed

  • Exploring LLM Traces

    PostHog/posthog

    Official

    Debug and inspect LLM/AI agent traces using PostHog's MCP tools.

    40k GitHub stars~4.4k tokensUpdated today
    Auto-check passed

  • Investigate Metric

    PostHog/posthog

    Official

    Diagnose why a product metric changed (dropped, spiked, or plateaued) by orchestrating breakdowns, actors, paths, lifecycle, retention, and annotations queries.

    40k GitHub stars~1.9k tokensUpdated today
    Auto-check passed

Works with

Categories

Questions about Writing Tests

What does Writing Tests do?

Gates whether a new test should exist and forces it to be efficient, protecting CI from low-value test bloat. Writing Tests is an agent skill from PostHog/posthog, published by the product's own GitHub organization. Gates whether a new test should exist and forces it to be efficient, protecting CI from low-value test bloat.

When should I use Writing Tests?

Writing Tests fits situations like: tasks that involve Unit testing; tasks that involve Failing and flaky tests; tasks that involve Backend development.

How do I install Writing Tests in Claude Code?

Run `npx skills add PostHog/posthog --skill writing-tests -a claude-code`. Or copy the skill folder (.agents/skills/writing-tests in PostHog/posthog) into .claude/skills/writing-tests in your project. Claude Code loads it when a task matches its description.

How do I install Writing Tests in Codex?

Run `npx skills add PostHog/posthog --skill writing-tests -a codex`. Or copy the skill folder (.agents/skills/writing-tests in PostHog/posthog) into .agents/skills/writing-tests in your project. Codex loads it when a task matches its description.

Can I use Writing Tests 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 PostHog/posthog --skill writing-tests -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/writing-tests, .gemini/skills/writing-tests, .github/skills/writing-tests and .opencode/skills/writing-tests in your project.

What does Writing Tests need to run?

SKILL.md names no scripts, command-line tools or credentials: Writing Tests is instructions for the agent only. Our summary lists: Python 3.

Does Writing Tests access the network?

SKILL.md names 2 domains. As links in the text: testing.googleblog.com and posthog.com. This is read from the text; nothing was executed.

Is Writing Tests 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 Writing Tests use?

Writing Tests has a licence file (the repository's licence) that doesn't match a standard licence. Read it on GitHub before reusing the skill.

How many tokens does Writing Tests use?

About 5.9k tokens (SKILL.md is roughly 24k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 3.6k tokens, read only when the agent opens those files.

What are the alternatives to Writing Tests?

Skills that share tags, products or a category with Writing Tests: Designing Tests (CloudAI-X/claude-workflow-v2, 1.4k stars), Playwright Testing (chongdashu/vibejam-starter-pack, 149 stars), Playwright Testing (chongdashu/vibejam-starter-pack, 149 stars) and Pytest (mathiasertl/django-ca, 158 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Writing Tests?

PostHog (a GitHub organization, an official publisher) maintains it in PostHog/posthog, which has 40,182 GitHub stars. The repository holds 252 skills in this directory. The repository was last updated on October 8, 2026.

Source: PostHog/posthog on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.