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.
- $ npx jest
- $ yarn test
+ $ bun test
There's often no need for code changes.
- Bun internally re-writes imports from
@jest/globalsto use thebun:testequivalents. - If you're relying on Jest to inject
test,expect, etc. as globals, Bun does that too.
But if you'd rather switch to the bun:test imports, you can do that too.
import {test, expect} from "@jest/globals";
import {test, expect} from "bun:test";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.
Some notable missing features:
expect.extend()expect().toMatchInlineSnapshot()expect().toHaveReturned()
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 guide to inject browser APIs into the global scope. This guide relies on happy-dom, which is a leaner and faster alternative to jsdom.
At the moment jsdom does not work in Bun due to its internal use of V8 APIs. Track support for it here.
[test]
preload = ["./happy-dom.ts"]
Replace bail in your Jest config with the --bail CLI flag.
bun test --bail 3Replace collectCoverage with the --coverage CLI flag.
bun test --coverageReplace testTimeout with the --test-timeout CLI flag.
bun test --timeout 10000Many other flags become irrelevant or obsolete when using bun test.
transform— Bun supports TypeScript & JSX. Other file types can be configured with Plugins.extensionsToTreatAsEsmhaste— Bun uses it's own internal source mapswatchman,watchPlugins,watchPathIgnorePatterns— use--watchto run tests in watch modeverbose— setlogLevel: "debug"inbunfig.toml
Settings that aren't mentioned here are not supported or have no equivalent. Please file a feature request if something important is missing.
See also: