关于模拟DateTime有一个特别的注意事项。现在使用TypeMock…

DateTime的值。现在必须放置到一个变量中，以便正确地模拟。例如:

这行不通:

if ((DateTime.Now - message.TimeOpened.Value) > new TimeSpan(1, 0, 0))

然而，这样做:

var currentDateTime = DateTime.Now;
if ((currentDateTime - message.TimeOpened.Value) > new TimeSpan(1, 0, 0))

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

以下是我对这个问题的回答。我将“环境上下文”模式与IDisposable结合起来。你可以使用DateTimeProvider。当前在您的正常程序代码和测试中，您使用using语句覆盖范围。

using System;
using System.Collections.Immutable;


namespace ambientcontext {

public abstract class DateTimeProvider : IDisposable
{
    private static ImmutableStack<DateTimeProvider> stack = ImmutableStack<DateTimeProvider>.Empty.Push(new DefaultDateTimeProvider());

    protected DateTimeProvider()
    {
        if (this.GetType() != typeof(DefaultDateTimeProvider))
            stack = stack.Push(this);
    }

    public static DateTimeProvider Current => stack.Peek();
    public abstract DateTime Today { get; }
    public abstract DateTime Now {get; }

    public void Dispose()
    {
        if (this.GetType() != typeof(DefaultDateTimeProvider))
            stack = stack.Pop();
    }

    // Not visible Default Implementation 
    private class DefaultDateTimeProvider : DateTimeProvider {
        public override DateTime Today => DateTime.Today; 
        public override DateTime Now => DateTime.Now; 
    }
}
}

下面是如何在单元测试中使用上述DateTimeProvider

using System;
using Xunit;

namespace ambientcontext
{
    public class TestDateTimeProvider
    {
        [Fact]
        public void TestDateTime()
        {
            var actual = DateTimeProvider.Current.Today;
            var expected = DateTime.Today;

            Assert.Equal<DateTime>(expected, actual);

            using (new MyDateTimeProvider(new DateTime(2012,12,21)))
            {
                Assert.Equal(2012, DateTimeProvider.Current.Today.Year);

                using (new MyDateTimeProvider(new DateTime(1984,4,4)))
                {
                    Assert.Equal(1984, DateTimeProvider.Current.Today.Year);    
                }

                Assert.Equal(2012, DateTimeProvider.Current.Today.Year);
            }

            // Fall-Back to Default DateTimeProvider 
            Assert.Equal<int>(expected.Year,  DateTimeProvider.Current.Today.Year);
        }

        private class MyDateTimeProvider : DateTimeProvider 
        {
            private readonly DateTime dateTime; 

            public MyDateTimeProvider(DateTime dateTime):base()
            {
                this.dateTime = dateTime; 
            }

            public override DateTime Today => this.dateTime.Date;

            public override DateTime Now => this.dateTime;
        }
    }
}

一种简单的方法是注入VirtualTime。它可以让你控制时间。 首先安装VirtualTime

Install-Package VirtualTime

例如，这允许在所有对DateTime的调用上使时间加快5倍。Now或UtcNow

var DateTime = DateTime.Now.ToVirtualTime(5);

放慢时间(如放慢5倍)

var DateTime = DateTime.Now.ToVirtualTime(0.5);

让时间静止

var DateTime = DateTime.Now.ToVirtualTime(0);

回到过去还没有测试过

下面是一个测试示例:

[TestMethod]
public void it_should_make_time_move_faster()
{
    int speedOfTimePerMs = 1000;
    int timeToPassMs = 3000;
    int expectedElapsedVirtualTime = speedOfTimePerMs * timeToPassMs;
    DateTime whenTimeStarts = DateTime.Now;
    ITime time = whenTimeStarts.ToVirtualTime(speedOfTimePerMs);
    Thread.Sleep(timeToPassMs);
    DateTime expectedTime = DateTime.Now.AddMilliseconds(expectedElapsedVirtualTime - timeToPassMs);
    DateTime virtualTime = time.Now;

    Assert.IsTrue(TestHelper.AreEqualWithinMarginOfError(expectedTime, virtualTime, MarginOfErrorMs));
}

你可以在这里查看更多测试:

https://github.com/VirtualTime/VirtualTime/blob/master/VirtualTimeLib.Tests/when_virtual_time_is_used.cs

什么DateTime.Now.ToVirtualTime扩展给你是一个ITime的实例，你传递给一个依赖于ITime的方法/类。一些DateTime.Now.ToVirtualTime被设置在你选择的DI容器中

下面是注入类构造函数的另一个例子

public class AlarmClock
{
    private ITime DateTime;
    public AlarmClock(ITime dateTime, int numberOfHours)
    {
        DateTime = dateTime;
        SetTime = DateTime.UtcNow.AddHours(numberOfHours);
        Task.Run(() =>
        {
            while (!IsAlarmOn)
            {
                IsAlarmOn = (SetTime - DateTime.UtcNow).TotalMilliseconds < 0;
            }
        });
    }
    public DateTime SetTime { get; set; }
    public bool IsAlarmOn { get; set; }
}

[TestMethod]
public void it_can_be_injected_as_a_dependency()
{
    //virtual time has to be 1000*3.75 faster to get to an hour 
    //in 1000 ms real time
    var dateTime = DateTime.Now.ToVirtualTime(1000 * 3.75);
    var numberOfHoursBeforeAlarmSounds = 1;
    var alarmClock = new AlarmClock(dateTime, numberOfHoursBeforeAlarmSounds);
    Assert.IsFalse(alarmClock.IsAlarmOn);
    System.Threading.Thread.Sleep(1000);
    Assert.IsTrue(alarmClock.IsAlarmOn);
}

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

也许不太专业，但更简单的解决方案可以在消费者方法中创建一个DateTime参数。例如，不使用像SampleMethod这样的make方法，而是使用带参数的make SampleMethod1。SampleMethod1的测试更简单

public void SampleMethod()
    {
        DateTime anotherDateTime = DateTime.Today.AddDays(-10);
        if ((DateTime.Now-anotherDateTime).TotalDays>10)
        {

        }
    }
    public void SampleMethod1(DateTime dateTimeNow)
    {
        DateTime anotherDateTime = DateTime.Today.AddDays(-10);
        if ((dateTimeNow - anotherDateTime).TotalDays > 10)
        {

        }

    }