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---
name: Use snapshot testing in `bun test`
---
Bun's test runner supports Jest-style snapshot testing via `.toMatchSnapshot()`.
{% callout %}
The `.toMatchInlineSnapshot()` method is not yet supported.
{% /callout %}
```ts#snap.test.ts
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()` (`{ foo: "bar" }`) and write it to disk in a directory called `__snapshots__` that lives alongside the test file.
```sh
$ bun test test/snap
bun test v0.8.0 (9c68abdb)
test/snap.test.ts:
✓ snapshot [1.48ms]
1 pass
0 fail
snapshots: +1 added # note: the snapshot is created automatically the first run
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
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
// Bun Snapshot v1, https://goo.gl/fbAQLP
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
$ bun test
bun test v0.8.0 (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
$ bun test --update-snapshots
bun test v0.8.0 (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](/docs/test/mocks) for complete documentation on mocking with the Bun test runner.
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