# Jest partial snapshot matching

Now that we first looked at [snapshot testing](https://daily-dev-tips.com/posts/react-snapshot-testing-with-jest/), you might already have come across some weird use-cases.

For instance, what if your data returns a date object?
Or are your IDs dynamic and ever-changing?

This means only a part of our snapshot should match.

## Jest partial snapshot matching

Let's take the following test, for instance.

```js
test('snapshot testing', async () => {
  const randomFact = {
    id: Math.random().toString(36).slice(2),
    fact: 'Chris is writing about Jest',
    createdAt: new Date(),
  };

  expect(randomFact).toMatchSnapshot();
});
```

If we run this code, our snapshot will be generated nicely, and the test will succeed.

```js
exports[`snapshot testing 1`] = `
Object {
  "createdAt": 2022-03-30T04:36:39.987Z,
  "fact": "Chris is writing about Jest",
  "id": "eq8b6a67yjb",
}
`;
```

However, what do you think will happen on the next run?
Correct, it will fail on both the `createdAt` and the `id` since those will be different.

![Failing snapshot](https://cdn.hashnode.com/res/hashnode/image/upload/v1648615075808/KTo7vlfMZ.png)

To fix this, we have to make sure Jest knows that the `createdAt` can be any date, and the ID can be any string type.

Luckily for us, it comes with this function, inside the `toMatchSnapshot` function you can define what objects should be made of like this:

```js
test('snapshot testing', async () => {
  const randomFact = {
    id: Math.random().toString(36).slice(2),
    fact: 'Chris is writing about Jest',
    createdAt: new Date(),
  };

  expect(randomFact).toMatchSnapshot({
    id: expect.any(String),
    createdAt: expect.any(Date),
  });
});
```

Note how we didn't add the `fact`. This means this will still check uniquely for each snapshot.

Now make sure to run your next test while passing the update flag.

```bash
npm run test -u
```

And after the update, your snapshot should look like this:

```js
exports[`snapshot testing 1`] = `
Object {
  "createdAt": Any<Date>,
  "fact": "Chris is writing about Jest",
  "id": Any<String>,
}
`;
```

Perfect!
We now have a unique date check on the `createdAt` field and a string check for the `id`.

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