jest_lint

Lint your Jest unit tests to find problems. Built with Rust.

Features

• Mock checking -- checks that all imports in the module under test have a corresponding jest.mock() in the test file
• Flagged expect args -- flags suspect words (e.g. "stub") inside expect() calls, since stub values shouldn't be asserted on

All features are enabled by default. Use .jest_lint.json to customize behavior.

Getting started

First: Install Rust and Cargo

Then, either install the published crate (easy) or download from this repo.

Install published crate (easy)

cargo install jest_lint
jest_lint --help

Check all files in the current directory:

jest_lint

Check a specific directory:

jest_lint -d path/to/files

Check specific files:

jest_lint -f path/to/foobar.test.js
jest_lint path/to/foo.test.js path/to/bar.test.js

Latest development build

Download this repository.

cd jest_lint
cargo run -- --help

PRs welcome!

Configuration

Create a .jest_lint.json file in your project root. The config file is automatically discovered by searching up from the checked file's directory.

{
  "ignoredModules": [
    "zod",
    "@mui/**",
    "*.module.scss",
    "next/**",
    "**/types/*"
  ],
  "expectArgs": {
    "flagged": ["stub"],
    "severity": "warning"
  }
}

Ignored modules

Patterns support exact matches and glob syntax (* for single level, ** for nested paths).

You can also ignore individual imports inline in your test file with a comment:

// jest_lint:ignore ./utils

Flagged expect args

Flags lines where expect() contains a word from the flagged list. This catches cases where stub values leak into assertions, e.g. expect(stubName).toBe("hello").

Field	Default	Description
enabled	true	Set to false to disable this check
flagged	[]	Words to flag inside expect() calls
severity	"error"	"error" (exit 1) or "warning" (exit 0)

See the examples directory for a working demo.

Tips & Tricks

If you're using VS Code, you can add a task to .vscode/tasks.json to run jest_lint on the current file:

{
  "label": "jest_lint",
  "type": "shell",
  "command": "jest_lint -f ${file}"
}

Then you can use a keyboard shortcut to check your mocks while you have your .spec.* or .test.* file open.