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Migrate from Jest to Bun's test runner

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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 # [!code --]
yarn test # [!code --]
bun test # [!code ++]

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.

test.ts
import { test, expect } from "@jest/globals"; // [!code --]
import { test, expect } from "bun:test"; // [!code ++]

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
global.d.ts
/// <reference types="bun-types/test-globals" />

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

math.test.ts
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.

bunfig.toml
[test]
preload = ["./happydom.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 module resolver
  • watchman, watchPlugins, watchPathIgnorePatterns — use --watch to run tests in watch mode
  • verbose — bun test reports each test by default. Use --only-failures or --dots for less output (see Test reporters).

Many other settings have an equivalent in the [test] section of bunfig.toml. For example:

  • setupFiles/setupFilesAfterEnv → preload
  • testPathIgnorePatterns → pathIgnorePatterns
  • rootDir → root
  • coverageDirectory → coverageDir
  • coverageReporters → coverageReporter
  • coverageThreshold → coverageThreshold (as a fraction like 0.9, not a percentage)

See Test configuration. Settings without an equivalent are not supported. File a feature request if something you need is missing.

See also: