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https://github.com/oven-sh/bun
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126 lines
3.7 KiB
Plaintext
126 lines
3.7 KiB
Plaintext
---
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title: Migrate from Jest to Bun's test runner
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sidebarTitle: Migrate from Jest
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mode: center
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---
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In many cases, Bun's test runner can run Jest test suites with no code changes. Just run `bun test` instead of `npx jest`, `yarn test`, etc.
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```sh terminal icon="terminal"
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npx jest # [!code --]
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yarn test # [!code --]
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bun test # [!code ++]
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```
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---
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There's often no need for code changes.
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- Bun internally re-writes imports from `@jest/globals` to use the `bun:test` equivalents.
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- If you're relying on Jest to inject `test`, `expect`, etc. as globals, Bun does that too.
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But if you'd rather switch to the `bun:test` imports, you can do that too.
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```ts title="test.ts" icon="/icons/typescript.svg"
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import { test, expect } from "@jest/globals"; // [!code --]
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import { test, expect } from "bun:test"; // [!code ++]
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```
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---
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Since Bun v1.2.19, you can enable **TypeScript support** for global test functions with a single triple-slash directive. This makes migrating from Jest even easier since you only need to add the directive once in your entire project:
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Add this directive to _just one file_ in your project, such as:
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- A `global.d.ts` file in your project root
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- Your test `preload.ts` setup file (if using `preload` in bunfig.toml)
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- Any single `.ts` file that TypeScript includes in your compilation
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```ts title="global.d.ts" icon="/icons/typescript.svg"
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/// <reference types="bun-types/test-globals" />
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```
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---
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Once added, all test files in your project automatically get TypeScript support for Jest globals:
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```ts math.test.ts icon="/icons/typescript.svg"
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describe("my test suite", () => {
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test("should work", () => {
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expect(1 + 1).toBe(2);
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});
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beforeAll(() => {
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// setup code
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});
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afterEach(() => {
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// cleanup code
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});
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});
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```
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---
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Bun implements the vast majority of Jest's matchers, but compatibility isn't 100% yet. Refer to the full compatibility table at [Docs > Test runner > Writing tests](/test/writing-tests#matchers).
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Some notable missing features:
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- `expect().toHaveReturned()`
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---
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If you're using `testEnvironment: "jsdom"` to run your tests in a browser-like environment, you should follow the [DOM testing with Bun and happy-dom](/guides/test/happy-dom) guide to inject browser APIs into the global scope. This guide relies on [`happy-dom`](https://github.com/capricorn86/happy-dom), which is a leaner and faster alternative to [`jsdom`](https://github.com/jsdom/jsdom).
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At the moment jsdom does not work in Bun due to its internal use of V8 APIs. Track support for it [here](https://github.com/oven-sh/bun/issues/3554).
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```toml bunfig.toml icon="settings"
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[test]
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preload = ["./happy-dom.ts"]
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```
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---
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Replace `bail` in your Jest config with the `--bail` CLI flag.
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```sh terminal icon="terminal"
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bun test --bail=3
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```
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---
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Replace `collectCoverage` with the `--coverage` CLI flag.
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```sh terminal icon="terminal"
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bun test --coverage
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```
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---
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Replace `testTimeout` with the `--test-timeout` CLI flag.
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```sh terminal icon="terminal"
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bun test --timeout 10000
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```
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---
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Many other flags become irrelevant or obsolete when using `bun test`.
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- `transform` — Bun supports TypeScript & JSX. Other file types can be configured with [Plugins](/runtime/plugins).
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- `extensionsToTreatAsEsm`
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- `haste` — Bun uses it's own internal source maps
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- `watchman`, `watchPlugins`, `watchPathIgnorePatterns` — use `--watch` to run tests in watch mode
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- `verbose` — set `logLevel: "debug"` in [`bunfig.toml`](/runtime/bunfig#loglevel)
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---
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Settings that aren't mentioned here are not supported or have no equivalent. Please [file a feature request](https://github.com/oven-sh/bun) if something important is missing.
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---
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See also:
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- [Mark a test as a todo](/guides/test/todo-tests)
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- [Docs > Test runner > Writing tests](/test/writing-tests)
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