> ## Documentation Index
> Fetch the complete documentation index at: https://bun-1dd33a4e-farm-15490b5d-test-done-error-hook.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Use snapshot testing in `bun test`

Bun's test runner supports Jest-style snapshot testing via `.toMatchSnapshot()`.

```ts snap.test.ts icon="https://mintcdn.com/bun-1dd33a4e-farm-15490b5d-test-done-error-hook/dtyJFOORXktpqgAt/icons/typescript.svg?fit=max&auto=format&n=dtyJFOORXktpqgAt&q=85&s=d88c07e26cef48a230df2faee376b314" theme={null}
import { test, expect } from "bun:test";

test("snapshot", () => {
  expect({ foo: "bar" }).toMatchSnapshot();
});
```

***

The first time this test is executed, Bun will evaluate the value passed into `expect()` and write it to disk in a directory called `__snapshots__` that lives alongside the test file. (Note the `snapshots: +1 added` line in the output.)

```sh terminal icon="terminal" theme={null}
bun test test/snap
```

```txt theme={null}
test/snap.test.ts:
✓ snapshot [1.48ms]

 1 pass
 0 fail
 snapshots: +1 added
 1 expect() calls
Ran 1 tests across 1 files. [82.00ms]
```

***

The `__snapshots__` directory contains a `.snap` file for each test file in the directory.

```txt File Tree icon="folder-tree" theme={null}
test
├── __snapshots__
│   └── snap.test.ts.snap
└── snap.test.ts
```

***

The `snap.test.ts.snap` file is a JavaScript file that exports a serialized version of the value passed into `expect()`. The `{foo: "bar"}` object has been serialized to JSON.

```js snap.test.ts.snap icon="file-code" theme={null}
// Bun Snapshot v1, https://bun.com/docs/test/snapshots

exports[`snapshot 1`] = `
{
  "foo": "bar",
}
`;
```

***

Later, when this test file is executed again, Bun will read the snapshot file and compare it to the value passed into `expect()`. If the values are different, the test will fail.

```sh terminal icon="terminal" theme={null}
bun test
```

```txt theme={null}
bun test v1.3.3 (9c68abdb)
test/snap.test.ts:
✓ snapshot [1.05ms]

 1 pass
 0 fail
 1 snapshots, 1 expect() calls
Ran 1 tests across 1 files. [101.00ms]
```

***

To update snapshots, use the `--update-snapshots` flag.

```sh terminal icon="terminal" theme={null}
bun test --update-snapshots
```

```txt theme={null}
bun test v1.3.3 (9c68abdb)
test/snap.test.ts:
✓ snapshot [0.86ms]

 1 pass
 0 fail
 snapshots: +1 added  # the snapshot was regenerated
 1 expect() calls
Ran 1 tests across 1 files. [102.00ms]
```

***

See [Docs > Test Runner > Snapshots](/test/snapshots) for complete documentation on snapshots with the Bun test runner.