element-android-Github/docs/database_migration_test.md

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<!--- TOC -->
* [Testing database migration](#testing-database-migration)
* [Creating a reference database](#creating-a-reference-database)
* [Testing](#testing)
<!--- END -->
## Testing database migration
### Creating a reference database
Databases are encrypted, the key to decrypt is needed to setup the test.
A special build property must be enabled to extract it.
Set `vector.debugPrivateData=true` in `~/.gradle/gradle.properties` (to avoid committing by mistake)
Launch the app in your emulator, login and use the app to fill up the database.
Save the key for the tested database
```
RealmKeysUtils W Database key for alias `session_db_fe9f212a611ccf6dea1141777065ed0a`: 935a6dfa0b0fc5cce1414194ed190....
RealmKeysUtils W Database key for alias `crypto_module_fe9f212a611ccf6dea1141777065ed0a`: 7b9a21a8a311e85d75b069a343.....
```
Use the [Device File Explorer](https://developer.android.com/studio/debug/device-file-explorer) to extrat the database file from the emulator.
Go to `data/data/im.vector.app.debug/files/<hash>/`
Pick the database you want to test (name can be found in SessionRealmConfigurationFactory):
- crypto_store.realm for crypto
- disk_store.realm for session
- etc...
Download the file on your disk
### Testing
Copy the file in `src/AndroidTest/assets`
see `CryptoSanityMigrationTest` or `RealmSessionStoreMigration43Test` for sample tests.
There are already some databases in the assets folder.
The existing test will properly detect schema changes, and fail with such errors if a migration is missing:
```
io.realm.exceptions.RealmMigrationNeededException: Migration is required due to the following errors:
- Property 'CryptoMetadataEntity.foo' has been added.
```
If you want to test properly more complex database migration (dynamic transforms) ensure that the database contains
the entity you want to migrate.
You can explore the database with [realm studio](https://www.mongodb.com/docs/realm/studio/) if needed.