Unit testing private methods

1.cs

public class Customer
{
    private CustomerStatus _status = CustomerStatus.Regular;

    public void Promote()
    {
        _status = CustomerStatus.Preferred;
    }

    public decimal GetDiscount()
    {
        return _status == CustomerStatus.Preferred ? 0.05m : 0m;
    }
}

public enum CustomerStatus
{
    Regular,
    Preferred
}

2.cs

public class Order
{
    private Customer _customer;
    private List<Product> _products;

    public string GenerateDescription()
    {
        return $"Customer name: {_customer.Name}, " +
            $"total number of products: {_products.Count}, " +
            $"total price: {GetPrice()}";
    }

    private decimal GetPrice()
    {
        decimal basePrice = /* Calculate based on _products */;
        decimal discounts = /* Calculate based on _customer */;
        decimal taxes = /* Calculate based on _products */;
        return basePrice - discounts + taxes;
    }
}

3.cs

public class Order
{
    private Customer _customer;
    private List<Product> _products;

    public string GenerateDescription()
    {
        var calculator = new PriceCalculator();

        return $"Customer name: {_customer.Name}, " +
            $"total number of products: {_products.Count}, " +
            $"total price: {calculator.Calculate(_customer, _products)}";
    }
}

public class PriceCalculator
{
    public decimal Calculate(Customer customer, List<Product> products)
    {
        decimal basePrice = /* Calculate based on products */;
        decimal discounts = /* Calculate based on customer */;
        decimal taxes = /* Calculate based on products */;
        return basePrice - discounts + taxes;
    }
}

4.cs

public class Order
{
    public void CheckOut(OrderStatistics orderStatistics)
    {
        /* other work */
        decimal totalAmount = /* calculate */;
        orderStatistics.LogOrder(_customer.Id, totalAmount);
    }
}

public class OrderStatistics
{
    private List<LogEntry> _log;

    public void LogOrder(int customerId, decimal amount)
    {
        _log.Add(new LogEntry(customerId, amount));
    }
}

5.cs

public class CheckOutHandler
{
    public void Handle()
    {
        Order order = /* get an order */;
        OrderStatistics orderStatistics = /* get order statistics */;
        (int customerId, decimal amount) = order.CheckOut();
        orderStatistics.LogOrder(customerId, amount);
    }
}

public class Order
{
    public (int customerId, decimal amount) CheckOut()
    {
        /* other work */
        decimal totalAmount = /* calculate */;
        return (_customer.Id, totalAmount);
    }
}

public class OrderStatistics
{
    private List<LogEntry> _log;

    public void LogOrder(int customerId, decimal amount)
    {
        _log.Add(new LogEntry(customerId, amount));
    }
}