Web Application Testing
anthropics/skills
Tests local web applications with Python Playwright scripts, checking frontend behavior, capturing screenshots and reading browser console logs.
Writes behavior-focused tests using Testing Trophy model with real dependencies.
Install Writing Tests
$ npx skills add rileyhilliard/claude-essentials --skill writing-tests -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install rileyhilliard/claude-essentials writing-tests --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/rileyhilliard/claude-essentials.git skills-src && mkdir -p .claude/skills && cp -r skills-src/plugins/ce/skills/writing-tests .claude/skills/writing-tests && rm -rf skills-srcUse ~/.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/
Install the "writing-tests" agent skill from https://github.com/rileyhilliard/claude-essentials/tree/main/plugins/ce/skills/writing-tests into .claude/skills/writing-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "writing-tests", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/rileyhilliard/claude-essentials/tree/main/plugins/ce/skills/writing-testsType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add rileyhilliard/claude-essentials --skill writing-tests -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install rileyhilliard/claude-essentials writing-tests --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/rileyhilliard/claude-essentials.git skills-src && mkdir -p .agents/skills && cp -r skills-src/plugins/ce/skills/writing-tests .agents/skills/writing-tests && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "writing-tests" agent skill from https://github.com/rileyhilliard/claude-essentials/tree/main/plugins/ce/skills/writing-tests into .agents/skills/writing-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "writing-tests", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add rileyhilliard/claude-essentials --skill writing-tests -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install rileyhilliard/claude-essentials writing-tests --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/rileyhilliard/claude-essentials.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/plugins/ce/skills/writing-tests .cursor/skills/writing-tests && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "writing-tests" agent skill from https://github.com/rileyhilliard/claude-essentials/tree/main/plugins/ce/skills/writing-tests into .cursor/skills/writing-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "writing-tests", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/rileyhilliard/claude-essentials.git --path plugins/ce/skills/writing-tests--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add rileyhilliard/claude-essentials --skill writing-tests -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install rileyhilliard/claude-essentials writing-tests --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/rileyhilliard/claude-essentials.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/plugins/ce/skills/writing-tests .gemini/skills/writing-tests && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "writing-tests" agent skill from https://github.com/rileyhilliard/claude-essentials/tree/main/plugins/ce/skills/writing-tests into .gemini/skills/writing-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "writing-tests", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install rileyhilliard/claude-essentials writing-testsInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add rileyhilliard/claude-essentials --skill writing-tests -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/rileyhilliard/claude-essentials.git skills-src && mkdir -p .github/skills && cp -r skills-src/plugins/ce/skills/writing-tests .github/skills/writing-tests && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "writing-tests" agent skill from https://github.com/rileyhilliard/claude-essentials/tree/main/plugins/ce/skills/writing-tests into .github/skills/writing-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "writing-tests", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add rileyhilliard/claude-essentials --skill writing-tests -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install rileyhilliard/claude-essentials writing-tests --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/rileyhilliard/claude-essentials.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/plugins/ce/skills/writing-tests .opencode/skills/writing-tests && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "writing-tests" agent skill from https://github.com/rileyhilliard/claude-essentials/tree/main/plugins/ce/skills/writing-tests into .opencode/skills/writing-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "writing-tests", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
writing-tests- GitHub stars
- 130
- Token cost
- ~999 tokens
- SKILL.md length
- 336 words
- Files
- 6 (incl. references)
- Skills in repo
- 17
- Repo updated
- First seen
- Licence
- MIT
At a glance
Writes behavior-focused tests using Testing Trophy model with real dependencies.
- Choosing test types
- SKILL.md covers Testing Trophy Model, Mocking Guidelines, Test Type Decision and Assertion Strategy, plus 4 more sections
- Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
- Avoiding anti-patterns like testing mocks
What it does
Writing Tests is an agent skill from rileyhilliard/claude-essentials. Writes behavior-focused tests using Testing Trophy model with real dependencies. Use when writing tests, choosing test types, or avoiding anti-patterns like testing mocks.
Its SKILL.md is about 1000 tokens, which your agent loads only when the skill is triggered. The skill folder holds 6 other files, including reference files (for example `references/go.md`, `references/python.md` and `references/typescript-react.md`).
It sits in Testing & QA. The licence is MIT.
When your agent uses it
- Choosing test types
- Avoiding anti-patterns like testing mocks
Example prompts
- “Use the writing-tests skill to write behavior-focused tests using Testing Trophy model with real dependencies”
- “/writing-tests”
What it can do on your machine
Read from SKILL.md and the folder at commit 3a67a01. 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 typescript).
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
Writing Tests loads about 999 tokens when it runs, and up to ~9.5k if it reads all its reference files. Until then it costs about 46 tokens; SKILL.md has 336 words of instructions outside code blocks.
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 rileyhilliard/claude-essentials at commit 3a67a01, republished under its MIT licence (© rileyhilliard). 336 words, ~999 tokens.
Download SKILL.mdSave it as
.claude/skills/writing-tests/SKILL.md (or your agent's skills folder). This skill also uses 5 other files; get the full folder from GitHub.- name
- writing-tests
- description
- Writes behavior-focused tests using Testing Trophy model with real dependencies. Use when writing tests, choosing test types, or avoiding anti-patterns like testing mocks.
If the current repo has its own rules/skills covering this topic (check .claude/rules/ and repo CLAUDE.md), those take precedence — apply this skill only where they're silent.
Writing Tests
Core principle: Test user-observable behavior with real dependencies. Tests should survive refactoring.
"The more your tests resemble the way your software is used, the more confidence they can give you." — Kent C. Dodds
Why this matters: Tests exist to give you confidence. The Testing Trophy prioritizes integration tests because they test real behavior across real modules — giving maximum confidence per test written. Unit tests in isolation often just test mocks, not your actual system.
Testing Trophy Model
| Priority | Type | When |
|---|---|---|
| 1st | Integration | Default - multiple units with real dependencies |
| 2nd | E2E | Complete user workflows |
| 3rd | Unit | Pure functions only (no dependencies) |
Mocking Guidelines
Default: Don't mock. Use real dependencies.
Only mock:
- External HTTP/API calls
- Time/randomness
- Third-party services (payments, email)
Never mock:
- Internal modules
- Database queries (use test DB)
- Business logic
- Your own code calling your own code
Before mocking, ask: "What side effects does this have? Does my test need those?" If unsure, run with real implementation first, then add minimal mocking only where needed.
Test Type Decision
Complete user workflow? → E2E test
Pure function (no side effects)? → Unit test
Everything else → Integration testAssertion Strategy
| Context | Assert On | Avoid |
|---|---|---|
| UI | Visible text, roles | CSS classes, internal state |
| API | Response body, status | Internal DB state |
| Library | Return values | Private methods |
Anti-Patterns
| Pattern | Fix |
|---|---|
| Testing mock calls | Test actual outcome |
| Test-only methods in production | Move to test utilities |
sleep(500) | Poll for actual condition |
| Asserting on internal state | Assert on observable output |
| Incomplete mocks | Mirror real API completely |
Quality Checklist
- Happy path covered
- Error conditions handled
- Real dependencies used (minimal mocking)
- Tests survive refactoring
- Test names describe behavior
Language-Specific Patterns
- JavaScript/Typescript/React: See references/typescript-react.md
- Python: See references/python.md
- Go: See references/go.md
Async Waiting
Wait for the actual condition, not a guess about how long it takes.
// Bad: arbitrary delay
await new Promise(r => setTimeout(r, 2000));
expect(element).toBeVisible();
// Good: poll for condition
await waitFor(() => expect(element).toBeVisible());Prefer framework built-ins:
- Testing Library:
findByqueries,waitFor - Playwright: auto-waiting,
expect(locator).toBeVisible() - pytest:
asyncio.wait_for, tenacity
Language-specific waiting patterns:
- TypeScript: See references/waiting-typescript.md
- Python: See references/waiting-python.md
Remember: Behavior over implementation. Real over mocked. Outputs over internals.
© rileyhilliard, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
SKILL.md and 5 other files (references) in plugins/ce/skills/writing-tests of rileyhilliard/claude-essentials.
- SKILL.md
- references/go.md
- references/python.md
- references/typescript-react.md
- references/waiting-python.md
- references/waiting-typescript.md
Open the folder on GitHubat commit 3a67a01
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.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| Writing Tests this skillrileyhilliard/claude-essentials | 130 | — | ~999 | Automated safety check: Pass | MIT | |
| Web Application Testinganthropics/skills | 180k | 51 repos | ~966 | Automated safety check: Pass | Apache-2.0 | |
| Diagnosing Bugsfossasia/eventyay-interpretation | 1.6k | 32 repos | ~2.1k | Automated safety check: Pass | Apache-2.0 | |
| TDDpietheinstrengholt/rssmonster | 564 | 30 repos | ~906 | Automated safety check: Pass | MIT | |
| TDD WorkflowhellangleZ/burn-in-cceverywhere-ralph | 112 | 11 repos | ~2.4k | Automated safety check: Pass | None | |
| TDDsanity-io/sanity | 6.4k | 20 repos | ~1k | Automated safety check: Pass | MIT |
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TDD
pietheinstrengholt/rssmonster
Test-driven development. An agent skill from pietheinstrengholt/rssmonster.
TDD Workflow
hellangleZ/burn-in-cceverywhere-ralph
A skill your agent uses when writing new features, fixing bugs, or refactoring code.
- Official
TDD
sanity-io/sanity
Test-driven development with red-green-refactor loop. An agent skill from sanity-io/sanity.
Context Driven Development
Ibrahim-3d/orchestrator-supaconductor
A skill your agent uses when working with Conductor's context-driven development methodology, managing project context artifacts, or understanding the relationship between product.md, tech-stack.md…
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Categories
Questions about Writing Tests
What does Writing Tests do?
Writes behavior-focused tests using Testing Trophy model with real dependencies. Writing Tests is an agent skill from rileyhilliard/claude-essentials. Writes behavior-focused tests using Testing Trophy model with real dependencies.
When should I use Writing Tests?
Writing Tests fits situations like: choosing test types; avoiding anti-patterns like testing mocks.
How do I install Writing Tests in Claude Code?
Run `npx skills add rileyhilliard/claude-essentials --skill writing-tests -a claude-code`. Or copy the skill folder (plugins/ce/skills/writing-tests in rileyhilliard/claude-essentials) 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 rileyhilliard/claude-essentials --skill writing-tests -a codex`. Or copy the skill folder (plugins/ce/skills/writing-tests in rileyhilliard/claude-essentials) 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 rileyhilliard/claude-essentials --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.
Does Writing Tests 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 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 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 Writing Tests use?
About 999 tokens (SKILL.md is roughly 4k 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 8.5k 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: Web Application Testing (anthropics/skills, 180k stars), Diagnosing Bugs (fossasia/eventyay-interpretation, 1.6k stars), TDD (pietheinstrengholt/rssmonster, 564 stars) and TDD Workflow (hellangleZ/burn-in-cceverywhere-ralph, 112 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Writing Tests?
rileyhilliard (a GitHub user) maintains it in rileyhilliard/claude-essentials, which has 130 GitHub stars. The repository holds 17 skills in this directory. The repository was last updated on August 18, 2026.
Source: rileyhilliard/claude-essentials on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.