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;
        }
    }
}

测试依赖于系统的代码。DateTime，系统.dll必须被模拟。

我知道有两个框架可以做到这一点。微软的假货和罩衫。

微软的假货需要visual studio 2012的最后通牒，直接从康普顿出来。

Smocks是一个开放源代码，非常容易使用。可以使用NuGet下载。

下面是System的一个模拟。DateTime:

Smock.Run(context =>
{
  context.Setup(() => DateTime.Now).Returns(new DateTime(2000, 1, 1));

   // Outputs "2000"
   Console.WriteLine(DateTime.Now.Year);
});

一个老问题，但仍然有效。

我的方法是创建一个新的接口和类来包装System.DateTime.Now调用

public interface INow
{
    DateTime Execute();
}

public sealed class Now : INow
{
    public DateTime Execute()
    {
        return DateTime.Now
    }
}

该接口可以注入到任何需要获取当前日期和时间的类中。在这个例子中，我有一个类，它将一个时间跨度添加到当前日期和时间(一个可测试的单元System.DateTime.Now.Add(timespan))

public interface IAddTimeSpanToCurrentDateAndTime
{
    DateTime Execute(TimeSpan input);
}

public class AddTimeSpanToCurrentDateAndTime : IAddTimeSpanToCurrentDateAndTime
{
    private readonly INow _now;

    public AddTimeSpanToCurrentDateAndTime(INow now)
    {
        this._now = now;
    }

    public DateTime Execute(TimeSpan input)
    {
        var currentDateAndTime = this._now.Execute();

        return currentDateAndTime.Add(input);
    }
}

并且可以编写测试以确保其正确运行。我使用NUnit和Moq，但任何测试框架都可以

public class Execute
{
    private Moq.Mock<INow> _nowMock;

    private AddTimeSpanToCurrentDateAndTime _systemUnderTest;

    [SetUp]
    public void Initialize()
    {
        this._nowMock = new Moq.Mock<INow>(Moq.MockBehavior.Strict);

        this._systemUnderTest = AddTimeSpanToCurrentDateAndTime(
            this._nowMock.Object);
    }

    [Test]
    public void AddTimeSpanToCurrentDateAndTimeExecute0001()
    {
        // arrange

        var input = new TimeSpan(911252);

        // arrange : mocks

        this._nowMock
            .Setup(a => a.Execute())
            .Returns(new DateTime(348756););

        // arrange : expected

        var expected = new DateTime(911252 + 348756);

        // act

        var actual = this._systemUnderTest.Execute(input).Result;

        // assert

        Assert.Equals(actual, expected);
    }
}

此模式适用于依赖于外部因素的任何函数，如System.Random.Next()， System.DateTime.Now。UtcNow, system . guide . newguid()等。

参见https://loadlimited.visualstudio.com/Stamina/_git/Stamina.Core获取更多示例或获取https://www.nuget.org/packages/Stamina.Core nuget包。

我也有同样的问题，但我在想我们不应该在同一类上使用设置日期时间的东西。因为有一天可能会导致滥用。我使用了提供商

public class DateTimeProvider
{
    protected static DateTime? DateTimeNow;
    protected static DateTime? DateTimeUtcNow;

    public DateTime Now
    {
        get
        {
            return DateTimeNow ?? System.DateTime.Now;
        }
    }

    public DateTime UtcNow
    {
        get
        {
            return DateTimeUtcNow ?? System.DateTime.UtcNow;
        }
    }

    public static DateTimeProvider DateTime
    {
        get
        {
            return new DateTimeProvider();
        }
    }

    protected DateTimeProvider()
    {       
    }
}

对于测试，在测试项目中创建了一个助手来处理设置的事情，

public class MockDateTimeProvider : DateTimeProvider
{
    public static void SetNow(DateTime now)
    {
        DateTimeNow = now;
    }

    public static void SetUtcNow(DateTime utc)
    {
        DateTimeUtcNow = utc;
    }

    public static void RestoreAsDefault()
    {
        DateTimeNow = null;
        DateTimeUtcNow = null;
    }
}

在代码

var dateTimeNow = DateTimeProvider.DateTime.Now         //not DateTime.Now
var dateTimeUtcNow = DateTimeProvider.DateTime.UtcNow   //not DateTime.UtcNow

在测试中

[Test]
public void Mocked_Now()
{
    DateTime now = DateTime.Now;
    MockDateTimeProvider.SetNow(now);    //set to mock
    Assert.AreEqual(now, DateTimeProvider.DateTime.Now);
    Assert.AreNotEqual(now, DateTimeProvider.DateTime.UtcNow);
}

[Test]
public void Mocked_UtcNow()
{
    DateTime utcNow = DateTime.UtcNow;
    MockDateTimeProvider.SetUtcNow(utcNow);   //set to mock
    Assert.AreEqual(utcNow, DateTimeProvider.DateTime.UtcNow);
    Assert.AreNotEqual(utcNow, DateTimeProvider.DateTime.Now);
}

但需要记住一件事，有时真正的DateTime和提供程序的DateTime并不相同

[Test]
public void Now()
{
    Assert.AreEqual(DateTime.Now.Kind, DateTimeProvider.DateTime.Now.Kind);
    Assert.LessOrEqual(DateTime.Now, DateTimeProvider.DateTime.Now);
    Assert.LessOrEqual(DateTimeProvider.DateTime.Now - DateTime.Now, TimeSpan.FromMilliseconds(1));
}

我假设差异是maximum TimeSpan.FromMilliseconds(0.00002)。但大多数时候甚至更少

在MockSamples中找到样本

这些都是很好的答案，这是我在另一个项目中所做的:

用法:

获取今天的真实日期时间

var today = SystemTime.Now().Date;

而不是使用DateTime。现在，你需要使用SystemTime.Now()…这并不难改变，但这种解决方案可能并不适合所有项目。

时间旅行(让我们去5年后)

SystemTime.SetDateTime(today.AddYears(5));

获得我们虚假的“今天”(从“今天”开始算起5年)

var fakeToday = SystemTime.Now().Date;

重置日期

SystemTime.ResetDateTime();

/// <summary>
/// Used for getting DateTime.Now(), time is changeable for unit testing
/// </summary>
public static class SystemTime
{
    /// <summary> Normally this is a pass-through to DateTime.Now, but it can be overridden with SetDateTime( .. ) for testing or debugging.
    /// </summary>
    public static Func<DateTime> Now = () => DateTime.Now;

    /// <summary> Set time to return when SystemTime.Now() is called.
    /// </summary>
    public static void SetDateTime(DateTime dateTimeNow)
    {
        Now = () =>  dateTimeNow;
    }

    /// <summary> Resets SystemTime.Now() to return DateTime.Now.
    /// </summary>
    public static void ResetDateTime()
    {
        Now = () => DateTime.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