余小章 @ 大內殿堂

/// <summary>
/// Class Order.
/// </summary>
public class Order
{
	/// <summary>
	/// 新增一筆訂單
	/// </summary>
	/// <param name="orderId">The source.</param>
	public void AddOneOrder(string orderId)
	{
		Contract.Requires<ArgumentNullException>(!string.IsNullOrWhiteSpace(orderId), "orderId");
		Contract.Ensures(orderId=="yao");
	}

	/// <summary>
	/// Tests the specified array.
	/// </summary>
	/// <param name="orderIds">The order ids.</param>
	/// <param name="orderId">The order identifier.</param>
	/// <returns>List&lt;System.String&gt;.</returns>
	public List<string> AddOneOrder(List<string> orderIds, string orderId)
	{
		Contract.Requires<ArgumentNullException>(orderIds != null, "orderIds");
		Contract.Requires<ArgumentNullException>(!string.IsNullOrWhiteSpace(orderId), "orderId");

		Contract.Ensures(orderIds.Count == Contract.OldValue(orderIds.Count) + 1);
		orderIds.Add(orderId);
		return orderIds;
	}
}

Build vNext via Visual Studio 2015

Visual Studio Version：Visual Studio 2015