Jest environment inspection

Version baseline: Jest 30.x, with 30.4.2 as the current stable release at this review. Inspect the installed patch, Node.js support, module system, test environment, and transformer compatibility before changing configuration.

Build a factual map of the project's Jest setup before changing or running anything. This skill is read-only unless the user explicitly asks to repair the environment.

Inspection workflow

1. Establish the project root. Look for package.json, lockfiles, workspace declarations, and the nearest repository instructions. Do not assume the current directory is the package that owns the tests.

2. Identify the package manager from the lockfile and package metadata: package-lock.json → npm, yarn.lock → Yarn, pnpm-lock.yaml → pnpm, bun.lock or bun.lockb → Bun. In a workspace, identify the package that owns the test file and its root command.

3. Read the relevant package.json scripts and dev dependencies. Prefer the existing test, test:watch, test:ci, or package-specific script over an invented direct command.

4. Check the installed Jest version through the project runner:

   npm exec -- jest --version
   # or: yarn jest --version
   # or: pnpm exec jest --version
   # or: bunx jest --version
   

   If the command cannot resolve Jest, report the package and version evidence; do not install it unless asked.

5. Locate configuration without guessing which file wins. Check jest.config.*, a jest field in package.json, workspace project configs, and script-level --config flags. Then use jest --showConfig through the project runner to inspect the resolved configuration.

6. Record the effective rootDir, testMatch or testRegex, ignored paths, testEnvironment, transform, moduleNameMapper, setup files, projects, coverage settings, and mock-reset settings.

7. List likely test files and confirm discovery with:

   <project-jest-command> --listTests
   

   Use --collectTests when the installed Jest version supports it and test names, not only file paths, need to be inspected.

Report format

Return a compact environment report containing:

• project/package root and package manager;
• Node and Jest versions;
• the script used to invoke tests;
• config source and effective values that affect the request;
• discovered test count or representative paths;
• the smallest next command for the user's task;
• any uncertainty, such as a workspace boundary or an unresolved transform.

Guardrails

• Never edit package.json, lockfiles, Jest config, setup files, or test files as part of inspection.
• Never treat a missing local Jest binary as permission to use a global binary; global Jest can use a different version and config.
• If a script chains other tools, show the complete script and explain where Jest arguments must be inserted.

References

• Jest CLI options
• Jest configuration