bun.sh/docs/cli/test.md

Bun ships with a fast built-in test runner. Tests are executed with the Bun runtime, and support the following features.

• TypeScript and JSX
• Lifecycle hooks
• Snapshot testing
• UI & DOM testing
• Watch mode with --watch
• Script pre-loading with --preload

Run tests

$ bun test

Tests are written in JavaScript or TypeScript with a Jest-like API. Refer to Writing tests for full documentation.

import { expect, test } from "bun:test";

test("2 + 2", () => {
  expect(2 + 2).toBe(4);
});

The runner recursively searches the working directory for files that match the following patterns:

• *.test.{js|jsx|ts|tsx}
• *_test.{js|jsx|ts|tsx}
• *.spec.{js|jsx|ts|tsx}
• *_spec.{js|jsx|ts|tsx}

You can filter the set of tests to run by passing additional positional arguments to bun test. Any file in the directory with an absolute path that contains one of the filters will run. Commonly, these filters will be file or directory names; glob patterns are not yet supported.

$ bun test <filter> <filter> ...

The test runner runs all tests in a single process. It loads all --preload scripts (see Lifecycle for details), then runs all tests. If a test fails, the test runner will exit with a non-zero exit code.

Watch mode

Similar to bun run, you can pass the --watch flag to bun test to watch for changes and re-run tests.

$ bun test --watch

Lifecycle hooks

Bun supports the following lifecycle hooks:

Hook	Description
beforeAll	Runs once before all tests.
beforeEach	Runs before each test.
afterEach	Runs after each test.
afterAll	Runs once after all tests.

These hooks can be define inside test files, or in a separate file that is preloaded with the --preload flag.

$ bun test --preload ./setup.ts

See Test > Lifecycle for complete documentation.

Mocks

Create mocks with the mock function. Mocks are automatically reset between tests.

import { test, expect, mock } from "bun:test";
const random = mock(() => Math.random());

test("random", async () => {
  const val = random();
  expect(val).toBeGreaterThan(0);
  expect(random).toHaveBeenCalled();
  expect(random).toHaveBeenCalledTimes(1);
});

See Test > Mocks for complete documentation.

Snapshot testing

Snapshots are supported by bun test. See Test > Snapshots for complete documentation.

UI & DOM testing

Bun is compatible with popular UI testing libraries:

• HappyDOM
• DOM Testing Library
• React Testing Library

See Test > DOM Testing for complete documentation.

Performance

Bun's test runner is fast.

{% image src="/images/buntest.jpeg" caption="Running 266 React SSR tests faster than Jest can print its version number." /%}