How to use flutter_test_config.dart

I'm trying to figure out how to use a flutter_test_config.dart file to configure a group of tests. Here is the code that I have in the file.

import 'dart:async';

import 'package:sqflite/sqflite.dart';
import 'package:mockito/mockito.dart';

class MockDatabase extends Mock implements Database {}

Future<void> main(FutureOr<void> testMain()) {
  final Database db = MockDatabase();
  testMain();
}

I would like to provide the db to the tests in this directory. What is the correct way to do this?