# Use snapshot testing in `bun test` (/docs/guides/test/snapshot)

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Related: [Run your tests with the Bun test runner](/docs/guides/test/run-tests.md), [Run tests in watch mode with Bun](/docs/guides/test/watch-mode.md), [Migrate from Jest to Bun's test runner](/docs/guides/test/migrate-from-jest.md), [Mock functions in `bun test`](/docs/guides/test/mock-functions.md), [Spy on methods in `bun test`](/docs/guides/test/spy-on.md), [Set the system time in Bun's test runner](/docs/guides/test/mock-clock.md)

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

```ts snap.test.ts icon="/icons/typescript.svg"
import { test, expect } from "bun:test";

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

***

The first time this test runs, Bun evaluates the value passed into `expect()` and writes it to a `__snapshots__` directory alongside the test file. (Note the `snapshots: +1 added` line in the output.)

```sh terminal icon="terminal"
bun test test/snap
```

```txt
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"
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"
// Bun Snapshot v1, https://bun.sh/docs/test/snapshots

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

***

On later runs, Bun reads the snapshot file and compares it to the value passed into `expect()`. If they differ, the test fails.

```sh terminal icon="terminal"
bun test
```

```txt
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"
bun test --update-snapshots
```

```txt
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 [Snapshots](/test/snapshots).