public async Task DeleteCollection()
        {
            var collection = new Collection("Important terms", "0");
            await mongo.AddCollection(collection);

            await mongo.DeleteCollection(collection.Id);

            Assert.IsNull(await mongo.FindCollection(collection.Id));
        }
        public static async Task Clear(this MongoCardStorage mongo)
        {
            foreach (var card in await mongo.GetAllCards())
            {
                await mongo.DeleteCard(card.Id);
            }

            foreach (var collection in await mongo.GetAllCollections())
            {
                await mongo.DeleteCollection(collection.Id);
            }
        }