Different security rules behavior between firestore(firebase-js-sdk) and @firebase/rules-unit-testing (also @firebase/testing).

### [REQUIRED] Describe your environment

* Operating System version: Mac OS Catalina 10.15.6
* Browser version: Google Chrome
* Firebase SDK version: 7.21.1
* Firebase Product: `firestore` / `rules-unit-testing`

### [REQUIRED] Describe the problem
For example, there is a collection includes following documents.

```
{
userId: 'userId',
data: null
}
```

Then, I created following security rules.
```
match /collectionName/{documentId} {
allow read: if resource.data.userId == request.auth.uid;
}
```

I can pass following test via `rules-unit-testing`. (I'm using `jest` and `ts-jest`)
```typescript
import * as testing from '@firebase/rules-unit-testing'

test('Should get document', () => {
const app = testing.initializeTestApp({ projectId: 'projectId', auth: { uid: 'userId' } })
// Following ref has a document like this { userId: 'userId' }.
const ref = app.firestore().collection('collectionName').doc('documentId').get()
return testing.assertSucceeds(ref.get())
})
```

However, I can't get data via `firebase/firestore`. (Permission denied error)
```typescript
firebase.firestore().collection('collectionName').doc('documentId').get()
```

Using following query, I can get data.
```typescript
firebase.firestore().collection('collectionName').where('userId', '==', firebase.auth().currentUser.uid)
```

I think this behavior(client sdk) is not wrong, but I don't know why test will be passed.