[Flutter] error writing flutter unit tests for an sqlite database api

I'm trying to write a test file for my flutter database api. I have a prepopulated database on wich i want to execute my tests that is stored in assets/database/ and is named database.db.

pubspec.yaml:

dev_dependencies:
flutter_lints: ^4.0.0
flutter_launcher_icons: ^0.13.1
flutter_test:
sdk: flutter
sqflite_common_ffi: ^2.3.3

flutter:
uses-material-design: true
generate: true
assets:
- assets/images/
- assets/database/


database_api.dart:

import 'dart:io';
import 'package:flutter/services.dart';
import 'packageath/path.dart';
import 'package:sqflite/sqflite.dart';

class DatabaseAPI {
static final DatabaseAPI _instance = DatabaseAPI._internal();
static Database? _db;
final String _dbName = "database.db";

DatabaseAPI._internal();

factory DatabaseAPI() {
return _instance;
}

Future<Database?> get db async {
if (_db != null) {
return _db;
} else {
_db = await _initDB();
return _db;
}
}

Future<Database> _initDB() async {
final path = join(await getDatabasesPath(), _dbName);
final exist = await databaseExists(path);
if(!exist) {
try {
ByteData data = await rootBundle.load(join('assets', 'database', _dbName));
List<int> bytes = data.buffer.asUint8List();
await File(path).writeAsBytes(bytes);
} catch (error) {
throw Exception('Error copying database: $error');
}
}
return await openDatabase(path);
}

Future<String> fetchLanguage() async {
var dbClient = await db;
final List<Map<String, Object?>> list = await dbClient!.query('language');
var lang = list[0]['selected'];
return lang.toString();
}
}


This is how i write my test file

database_api_test.dart:

import 'package:flutter_test/flutter_test.dart';
import 'package:drinking_game/db_api/database_api.dart';
import 'package:sqflite_common_ffi/sqflite_ffi.dart';

void main() {
TestWidgetsFlutterBinding.ensureInitialized();
databaseFactory = databaseFactoryFfi;

test('fetchLanguage returns correct data', () async {
var api = DatabaseAPI();
var lang = await api.fetchLanguage();
print(lang);
expect(lang, "Italiano");
});
}


The error that is generated is:

Exception: Error copying database: Unable to load asset: "assets\database\database.db".
The asset does not exist or has empty data.
package:drinking_game/db_api/new_database_api.dart 49:9 DatabaseAPI._initDB


But this error arise just when i run the test, when i do a normal build i have no error. How can i solve this?

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