qa-unit-tests-js

Action-taking agent that authors one JS/TS unit test file per spec - detects framework (Jest / Vitest / Mocha / Jasmine / AVA) from `package.json` devDependencies + config files (`jest.config.*`, `vitest.config.*`, `.mocharc.*`, `spec/support/jasmine.json`, package.json `ava` block), and pairs with `@faker-js/faker` or MSW handlers when present in deps. Distinct from `qa-shift-left/spec-to-suite-orchestrator` (language-agnostic multi-stage project-skeleton workflow) - narrower scope, single-file output, JavaScript/TypeScript only. Sibling of the per-language authors in `qa-unit-tests-{net,jvm,python,go-rust}` and `qa-desktop/desktop-test-author`. Use when adding a single new JS/TS unit test to an existing test project.

Configures and runs AVA - concurrent-by-default JS/TS test framework with isolated test files (each file runs in its own Node process), no globals (explicit `import test from 'ava'`), async-first API, snapshot support, and TypeScript via `@ava/typescript`. Use when the user wants minimal-API parallel-by-default tests, or works with libraries (vs apps) where per-file isolation prevents test interference.

Configures and runs Jasmine - the original BDD-style JS test framework (predecessor to Jest) with built-in matchers + spies, no external assertion library; ships `jasmine-core` + `jasmine` runner; `spec_dir` + `helpers` convention; `jasmine.json` config; spy patterns (`spyOn`, `createSpy`); pairs with Karma for in-browser testing. Use when the user maintains legacy AngularJS / Karma+Jasmine codebases, or wants minimal BDD-style tests with no third-party assertion library.

Configures and runs Jest - Meta-built batteries-included JS/TS unit framework with built-in `expect`, snapshot testing, mocking (`jest.mock`, `jest.fn`, `jest.spyOn`, manual `__mocks__/`), test environment selection (`jsdom` / `node`), parallel workers, coverage via Istanbul, watch mode, and CI integration via `--ci` flag. Use when the user works with React (CRA / older Next.js) or Node services and needs the most ecosystem-supported JS test framework.

Configures and runs Mocha - pluggable JS test runner pairable with Chai assertions, Sinon mocking, and nyc / c8 coverage; supports BDD interface (`describe` / `it`) and TDD interface (`suite` / `test`); async tests via callbacks / promises / async-await; `--parallel` mode (Mocha 8+); `.mocharc.json` config; per-test exclusivity via `.only()` / `.skip()`. Use when the user prefers a minimal pluggable runner (vs Jest's batteries-included) or maintains legacy Mocha codebases.

Configures and runs Vitest - Vite-native unit framework with Jest-compatible API (`expect`, `vi.fn`, `vi.mock`, `vi.spyOn`); reads `vite.config.*` so existing Vite plugins work; supports in-source testing via `if (import.meta.vitest)`, browser-mode UI for headed tests, type-checking via `vitest --typecheck`, native ESM, and coverage via v8 (default) or istanbul providers. Use when the user works with Vite-based projects (Vue, Svelte, Solid, modern React with Vite) or wants Jest-compatible API with faster Vite-native runs.