Unit Test小技巧 : DateTime的Stub

Posted on 2010-09-14 00:31 黃偉榮阅读(566) 评论(0) 编辑收藏举报

為什麼要寫一個DateTime的Stub呢?

在有些情況必需判斷今天，如不同的節日，不同的Logo，因為System.DateTime.Now或Today，沒有辦法模擬，寫Unit Test時就沒有辦法測各個時間點的反應，總不可能做個測試要改系統時間吧。

建立DateTImeProdiver的虛擬類別，來包裝DateTime，有二個實作DefaultDateTimeProdiver是一般的Code使用，TestDateTimeProvider是Test的Code使用。

圖一 DateTiemProdiver的類別圖

使用

所有呼叫System.DateTime.Now或Today，都改成用System.DateTimeProdiver.Current.Now或Today，為了方便測試，改變一點寫法不為過吧。

1	`DateTime today = DateTimeProvider.Current.Today;<br>`

測試時

//測試時改變DateTimeProvider的實例，以便摸擬不同時間的變化
DateTimeProvider.Current = new TestDateTimeProvider(new DateTime(2010, 1, 1));
Assert.AreEqual(LogoHelper.GetLogo(),"元旦.png");
 
DateTimeProvider.Current = new TestDateTimeProvider(new DateTime(2010, 2, 14));
Assert.AreEqual(LogoHelper.GetLogo(), "情人節.png");

原始碼

DateTImeProdiver與DefaultDateTimeProdiver

//使用System，方便呼叫
namespace System
{
    /// <summary>
    /// 為了單元測試增加的提供者，如DateTime.Now，無法Mock，所以多一層以便測試
    /// </summary>
    public abstract class DateTimeProvider
    {
        /// <summary>
        /// 預設的DateTimeProvider
        /// </summary>
        private class DefaultDateTimeProvider : DateTimeProvider
        {
            /// <summary>
            /// 使用獨體模式
            /// </summary>
            private static DateTimeProvider instance;
 
            static DefaultDateTimeProvider()
            {
                instance = new DefaultDateTimeProvider();
            }
 
            public static DateTimeProvider Instance
            {
                get
                {
                    return instance;
                }
            }
 
            public override DateTime Now
            {
                get { return DateTime.Now; }
            }
 
            public override DateTime UtcNow
            {
                get { return DateTime.UtcNow; }
            }
 
            public override DateTime Today
            {
                get { return DateTime.Today; }
            }            
        }
 
        /// <summary>
        /// 預設使用DefaultDateTimeProvider的獨體值
        /// </summary>
        private static DateTimeProvider current = DefaultDateTimeProvider.Instance;
 
        /// <summary>
        /// 可替換成別的DateTimeProvider
        /// </summary>
        public static DateTimeProvider Current
        {
            get { return DateTimeProvider.current; }
            set
            {
                if (value == null)
                {
                    throw new ArgumentNullException("value");
                }
 
                DateTimeProvider.current = value;
            }
        }
 
        public abstract DateTime Now { get; }
 
        public abstract DateTime UtcNow { get; }
 
        public abstract DateTime Today { get; }
    }
}

TestDateTImeProdiver

/// <summary>
/// 測試專用的DateTimeProvider
/// </summary>
public class TestDateTimeProvider : DateTimeProvider
{
    private DateTime datetime;
 
    public TestDateTimeProvider(DateTime datetime)
    {
        this.datetime = datetime;
    }
 
    public override DateTime Now
    {
        get { return datetime; }
    }
 
    public override DateTime UtcNow
    {
        get { return datetime.ToUniversalTime(); }
    }
 
    public override DateTime Today
    {
        get { return datetime.Date; }
    }
}