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.
npx agentmods add skills/vladolaru/claude-code-plugins/js-testing-patternsnpx skills add vladolaru/claude-code-plugins --skill js-testing-patternsgit clone --depth 1 https://github.com/vladolaru/claude-code-pluginsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/vladolaru/claude-code-plugins/js-testing-patterns)<a href="https://agentmods.dev/skills/vladolaru/claude-code-plugins/js-testing-patterns"><img src="https://agentmods.dev/badge/skills/vladolaru/claude-code-plugins/js-testing-patterns.svg" alt="Measured on agentmods" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00037 | $0.00976 |
| Opus 5 | $0.00018 | $0.00488 |
| Sonnet 5 | $0.00007 | $0.00195 |
| Haiku 4.5 | $0.00004 | $0.00098 |
Grade A, and why
js-testing-patterns 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 yesterday.
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.
How it starts
The opening of the file, as written. The whole thing — 70 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Skill Directory
Resolve SKILL_DIR to the absolute directory containing this SKILL.md, as
shown by the current host, before using any bundled path below.
Before a shell command uses $SKILL_DIR, assign it in that command or replace
it with the resolved path. It is not a host-exported environment variable.
JavaScript Testing Patterns
Jest, Vitest, and React Testing Library testing patterns. For shared test quality principles (philosophy, smells, mocking decisions), see testing-patterns.
Reference Routing
| Need | Reference File | Sections to Read |
|---|---|---|
| Jest/Vitest + RTL patterns | $SKILL_DIR/../testing-patterns/references/jest-vitest-patterns.md |
Full file (~422L, manageable) |
| Behavior vs implementation | $SKILL_DIR/../testing-patterns/references/test-philosophy.md |
## The Fundamental Shift + ## Four Core Principles |
| Flaky/brittle tests | $SKILL_DIR/../testing-patterns/references/test-smells.md |
## The Six Major Test Smells (relevant subsection) |
| Mock usage decisions | $SKILL_DIR/../testing-patterns/references/mocking-strategies.md |
## The Mocking Decision Framework |
| AAA pattern/naming | $SKILL_DIR/../testing-patterns/references/test-structure.md |
## The AAA Pattern + ## Test Naming Conventions |
| Test data strategy | $SKILL_DIR/../testing-patterns/references/test-data.md |
## Factories + ## Builders |
How to read sections: Grep for heading to find line number, Read with offset+limit.
RTL Query Priority (Best to Worst)
getByRole('button', { name: 'Submit' })— accessible, resilientgetByLabelText('Email')— form elementsgetByPlaceholderText()— when no labelgetByText('Click me')— visible contentgetByDisplayValue()— filled inputsgetByTestId('submit-btn')— last resort
JS Assertion Quick Reference
| Use | Instead Of | Why |
|---|---|---|
toMatchObject({key: val}) |
toEqual({...all fields}) |
Partial match, resilient to new fields |
toHaveBeenCalledWith(x) |
toHaveBeenCalled() |
Verifies correct arguments |
await expect(fn()).rejects.toThrow() |
Missing await |
Without await, assertion silently passes |
userEvent.click() |
fireEvent.click() |
Simulates real user interaction |
jest.useFakeTimers() |
Real timers | Deterministic, no flakiness |
toContainEqual(item) |
toEqual([...all items]) |
Checks membership, not exact array |
| Inline snapshots | toMatchSnapshot() on large output |
Reviewed in PR diff, not hidden files |
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.
- yesterday First seen · 70 lines · 37 tokens per session scan A d9b3d5348d9c
js-testing-patterns is a skill published in the GitHub repository vladolaru/claude-code-plugins (8 stars, last pushed yesterday), licensed MIT. It adds 37 tokens to every session and 976 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 2026-09-03.
Other skills, from other repositories
test-bridge
Bridge Server (TypeScript) のテスト実行・型チェック・テスト記述ガイド.
typescript
TypeScript strict mode with eslint and jest.
jest-unit
Unit testing skill using Jest for TypeScript and JavaScript, covering mocking, spies, snapshots, coverage, async testing, and custom matchers.
vitest-skill
Generates Vitest tests in JavaScript/TypeScript with Vite-native speed. Jest-compatible API with ESM support and HMR. Use when user mentions "Vitest", "vi.mock", "vitest.config". Triggers on: "Vitest", "vi.mock", "vi.fn", "Vite test", "vitest config".
typescript-testing
Applies repository-aware TypeScript test design, behavior evidence, isolation, and mock-boundary criteria. Use when writing or reviewing unit tests.
ts-library
Use when authoring TypeScript libraries or npm packages - covers project setup, package.json exports, build tooling (tsdown/unbuild), API design patterns, type inference tricks, testing, and publishing to npm. Use when bundling, configuring dual CJS/ESM output, or setting up release workflows.