Fix the provider declaration in Nest.js

Question

Consider the following code:
```ts
@Module({
  providers: [
    {
      provide: 'DATABASE_SERVICE',
      useFactory: (configService: ConfigService) => {
        return new DatabaseService(configService.get('DATABASE_URL'));
      }
    }
  ]
})
export class AppModule {}
```

What's wrong with the provider declaration?

Accepted Answer

The `inject` property needed to inject `ConfigService` into the `useFactory` function is missing.

Answer

The `DATABASE_SERVICE` key is not correctly formatted.

Answer

The `get` method cannot be used directly on `ConfigService`.

Answer

The module does not include import of the `ConfigService`.

Question from the Nest.js test

Fix the provider declaration in Nest.js