RefactoredUseCase.cs

namespace Domain
{
    public class UseCase
    {
        private readonly IPublisher _publisher;
        private readonly IRetrieveProducts _productsRetriever;

        public UseCase(
            IPublisher publisher,
            IRetrieveProducts productsRetriever)
        {
            _publisher = publisher;
            _productsRetriever = productsRetriever;
        }

        public async Task Run()
        {
            var products = await _productsRetriever.Get();

            foreach (var product in products)
            {
                product.CalculateReorderLevel();
                await _publisher.Publish(product);
            }
        }
    }
}