AVA

AVA is a Node.js test runner that lets you run JavaScript tests concurrently for faster feedback, with a clean and minimal API. Created by Sindre Sorhus in 2015, AVA has over 20,500 stars as of 2026 and differentiates itself from other JavaScript test frameworks (Jest, Mocha) by running each test file in a separate worker process, enabling true parallel test execution that leverages all available CPU cores. Key design principles include: no implicit globals (test, expect, and other functions must be explicitly imported, preventing test pollution), concurrent test execution (tests within a file run concurrently by default, with optional serial mode via test.serial for tests that must run sequentially), isolated test environment (each test file gets its own Node.js process with fresh module imports, eliminating state leakage between test files), TypeScript support out of the box (via esbuild-based transpilation, no ts-node required), ESM support (native ES module syntax without Babel), snapshot testing (with compatibility for updating and pruning obsolete snapshots), assertion library built-in (with detailed diff output for objects and arrays, and custom assertion messages), test hooks (before, after, beforeEach, afterEach with proper isolation), timeout configuration, watch mode (re-running only affected tests on file changes via tsserver integration), Markdown documentation testing (extracting and running code blocks from .md files), and CI integration with JUnit XML and TAP output formats. AVA's minimal configuration approach means tests can be written with zero config: just import {test} from 'ava' and start writing tests.