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    :x: :heavy_check_mark: A beautifully simple and capable test runner
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    • Simple - zero-config, no API to learn, out of the box ESM/CJS support
    • Lightweight - 6kB and no dependencies
    • Magical - simply export test functions, that's all
    • Blazingly fast - with almost zero abstractions, xv is as fast as Node
    • Unix philosophy™ - do one thing well, xv is only a test runner

    Used by lowdb (local JSON database), steno (fast file writer) and other awesome projects.


    npm install xv --save-dev


    Create a test file and use Node's built-in assert module:

    // src/add.test.js
    import { strict as assert } from 'assert'
    import add from './add.js'
    // This is plain Node code, there's no xv API
    export function testAdd() {
      assert.equal(add(1, 2), 3)

    Edit package.json:

      "scripts": {
        "test": "xv src"

    Run all test files:

    npm test

    Run a single test file:

    npx xv src/add.test.js


    When provided with a directory, xv will look for files named *.test.js or test.js and run exported functions sequentially.


    To test TypeScript code, compile your .ts files and run xv on compiled .js files.

    For example, assuming your compiled files are in lib/, edit package.json to run xv after tsc:

      "scripts": {
    -   "test": "xv src"
    +   "test": "tsc && xv lib"

    If you're publishing to npm, edit package.json to exclude compiled test files:

      "files": [
    +   "!lib/**/*.test.js",
    +   "!lib/**/test.js"

    Common JS

    xv can also test CJS code.

    // src/add.test.js
    const assert = require('assert').strict;
    const add = require('./add')
    // This is plain Node code, there's no xv API
    exports.testAdd = function() {
      assert.equal(add(1, 2), 3)

    Watch mode

    xv doesn't integrate a watch mode. If the feature is needed, it's recommended to use tools like watchexec or chokidar-cli to re-run xv when there are changes.


    The project being very simple by design, there probably won't be frequent updates to the code (which is a good thing for you, unless you like Dependabot alerts and updating devDependencies). It will be updated to support latest Node releases and implement potential improvements.

    tl;dr xv is maintained and used, even though code updates may not be recent.

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