Migrate from Jest to Bun's test runner

In many cases, Bun's test runner can run Jest test suites with no code changes. Run bun test instead of npx jest or yarn test.

$ npx jest
$ yarn test
$ bun test

Your test files usually work as-is.

• Bun internally rewrites imports from @jest/globals to their bun:test equivalents.
• If you rely on Jest to inject globals like test and expect, Bun does that too.

If you'd rather import from bun:test directly, update the imports.

import { test, expect } from "@jest/globals"; 
import { test, expect } from "bun:test"; 

Since Bun v1.2.19, a triple-slash directive enables TypeScript support for global test functions. Add it to one file in your project, such as:

• A global.d.ts file in your project root
• Your test preload.ts setup file (if using preload in bunfig.toml)
• Any single .ts file that TypeScript includes in your compilation

/// <reference types="bun-types/test-globals" />

Once added, every test file in your project gets TypeScript support for the Jest globals:

describe("my test suite", () => {
  test("should work", () => {
    expect(1 + 1).toBe(2);
  });

  beforeAll(() => {
    // setup code
  });

  afterEach(() => {
    // cleanup code
  });
});

Bun implements most of Jest's matchers, but compatibility isn't 100%. See the compatibility table in Writing tests.

If you use testEnvironment: "jsdom" to run your tests in a browser-like environment, follow the DOM testing with Bun and happy-dom guide to inject browser APIs into the global scope. That guide uses happy-dom, a leaner and faster alternative to jsdom.

[test]
preload = ["./happy-dom.ts"]

Replace bail in your Jest config with the --bail CLI flag.

$ bun test --bail=3

Replace collectCoverage with the --coverage CLI flag.

$ bun test --coverage

Replace testTimeout with the --timeout CLI flag.

$ bun test --timeout 10000

Many other Jest settings are irrelevant in bun test.

• transform — Bun supports TypeScript & JSX. Configure other file types with plugins.
• extensionsToTreatAsEsm
• haste — Bun uses its own internal source maps
• watchman, watchPlugins, watchPathIgnorePatterns — use --watch to run tests in watch mode
• verbose — set logLevel: "debug" in bunfig.toml

Settings that aren't mentioned here are not supported or have no equivalent. File a feature request if something you need is missing.

See also:

• Mark a test as a todo
• Writing tests