unittest-example-5.cs

public interface IInvoiceWriter
    {
        void Write(Invoice invoice);
    }
    
public class InvoiceWriter : IInvoiceWriter
    {
        private readonly IPrinter _printer;
        private readonly IPageLayout _layout;

        public InvoiceWriter(
            IPrinter printer, 
            IPageLayout layout)
        {
            _printer = printer;
            _layout = layout;
        }

        public void Write(Invoice invoice)
        {
            _printer.SetPageLayout(_layout);

            if (invoice.IsOverdue)
                _printer.SetInkColor("Red");

            _printer.WriteLine("Invoice ID: " + invoice.Id);

            // Remaining print statements would go here
        }
    }
    
     public class PrintInvoiceCommand
    {
        private readonly IDatabase _database;
        private readonly IInvoiceWriter _writer;

        public PrintInvoiceCommand(
            IDatabase database,
            IInvoiceWriter writer)
        {
            _database = database;
            _writer = writer;
        }

        public void Execute(int invoiceId)
        {
            var invoice = _database.GetInvoice(invoiceId);

            _writer.Write(invoice);
        }
    }