Bun ships with a built-in test runner.

## Run tests

```bash
$ bun test
```

Tests are written in JavaScript or TypeScript with a Jest-like API. Refer to [Writing tests](/docs/test/writing) for full documentation.

```ts#math.test.ts
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.

```bash
$ bun test <filter> <filter> ...
```

## Snapshot testing

Snapshots are supported by `bun test`. First, write a test using the `.toMatchSnapshot()` matcher:

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

test("snap", () => {
  expect("foo").toMatchSnapshot();
});
```

Then generate snapshots with the following command:

```bash
bun test --update-snapshots
```

Snapshots will be stored in a `__snapshots__` directory next to the test file.

## Watch mode

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

```bash
$ bun test --watch
```

## 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." /%}

<!--
Consider the following directory structure:

```
.
├── a.test.ts
├── b.test.ts
├── c.test.ts
└── foo
    ├── a.test.ts
    └── b.test.ts
```

To run both `a.test.ts` files:

```
$ bun test a
```

To run all tests in the `foo` directory:

```
$ bun test foo
```

Any test file in the directory with an _absolute path_ that contains one of the targets will run. Glob patterns are not yet supported. -->