我有一些单元测试,期望“当前时间”与DateTime不同。显然,我不想改变电脑的时间。

实现这一目标的最佳策略是什么?


当前回答

摩尔数:

[Test]  
public void TestOfDateTime()  
{  
      var firstValue = DateTime.Now;
      MDateTime.NowGet = () => new DateTime(2000,1,1);
      var secondValue = DateTime.Now;
      Assert(firstValue > secondValue); // would be false if 'moleing' failed
}

免责声明-我工作的鼹鼠

其他回答

您可以更改您正在测试的类使用Func<DateTime>,它将通过它的构造函数参数传递,因此当您在实际代码中创建类的实例时,您可以pass () => DateTime。UtcNow到Func<DateTime>参数,在测试中,您可以传递希望测试的时间。

例如:

    [TestMethod]
    public void MyTestMethod()
    {
        var instance = new MyClass(() => DateTime.MinValue);
        Assert.AreEqual(instance.MyMethod(), DateTime.MinValue);
    } 

    public void RealWorldInitialization()
    {
        new MyClass(() => DateTime.UtcNow);
    }

    class MyClass
    {
        private readonly Func<DateTime> _utcTimeNow;

        public MyClass(Func<DateTime> UtcTimeNow)
        {
            _utcTimeNow = UtcTimeNow;
        }

        public DateTime MyMethod()
        {
            return _utcTimeNow();
        }
    }

关于@crabcrusherclamcollector的回答,在EF查询中使用这种方法时存在问题。NotSupportedException: LINQ to Entities不支持LINQ表达式节点类型“Invoke”。我将实现修改为:

public static class SystemTime
    {
        private static Func<DateTime> UtcNowFunc = () => DateTime.UtcNow;

        public static void SetDateTime(DateTime dateTimeNow)
        {
            UtcNowFunc = () => dateTimeNow;
        }

        public static void ResetDateTime()
        {
            UtcNowFunc = () => DateTime.UtcNow;
        }

        public static DateTime UtcNow
        {
            get
            {
                DateTime now = UtcNowFunc.Invoke();
                return now;
            }
        }
    }

模拟对象。

一个模拟DateTime,返回适合您的测试的Now。

我们使用的是静态SystemTime对象,但是在运行并行单元测试时遇到了问题。我尝试使用Henk van Boeijen的解决方案,但在派生异步线程上有问题,最终以类似于下面的方式使用AsyncLocal:

public static class Clock
{
    private static Func<DateTime> _utcNow = () => DateTime.UtcNow;

    static AsyncLocal<Func<DateTime>> _override = new AsyncLocal<Func<DateTime>>();

    public static DateTime UtcNow => (_override.Value ?? _utcNow)();

    public static void Set(Func<DateTime> func)
    {
        _override.Value = func;
    }

    public static void Reset()
    {
        _override.Value = null;
    }
}

来源:https://gist.github.com/CraftyFella/42f459f7687b0b8b268fc311e6b4af08

好的做法是,当DateTimeProvider实现IDisposable时。

public class DateTimeProvider : IDisposable 
{ 
    [ThreadStatic] 
    private static DateTime? _injectedDateTime; 

    private DateTimeProvider() 
    { 
    } 

    /// <summary> 
    /// Gets DateTime now. 
    /// </summary> 
    /// <value> 
    /// The DateTime now. 
    /// </value> 
    public static DateTime Now 
    { 
        get 
        { 
            return _injectedDateTime ?? DateTime.Now; 
        } 
    } 

    /// <summary> 
    /// Injects the actual date time. 
    /// </summary> 
    /// <param name="actualDateTime">The actual date time.</param> 
    public static IDisposable InjectActualDateTime(DateTime actualDateTime) 
    { 
        _injectedDateTime = actualDateTime; 

        return new DateTimeProvider(); 
    } 

    public void Dispose() 
    { 
        _injectedDateTime = null; 
    } 
} 

接下来,您可以为单元测试注入假DateTime

    using (var date = DateTimeProvider.InjectActualDateTime(expectedDateTime)) 
    { 
        var bankAccount = new BankAccount(); 

        bankAccount.DepositMoney(600); 

        var lastTransaction = bankAccount.Transactions.Last(); 

        Assert.IsTrue(expectedDateTime.Equals(bankAccount.Transactions[0].TransactionDate)); 
    } 

参见示例DateTimeProvider示例