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

使用ThreadLocal<T>的线程安全SystemClock非常适合我。

ThreadLocal<T>在. net Framework v4.0及更高版本中可用。

/// <summary>
/// Provides access to system time while allowing it to be set to a fixed <see cref="DateTime"/> value.
/// </summary>
/// <remarks>
/// This class is thread safe.
/// </remarks>
public static class SystemClock
{
    private static readonly ThreadLocal<Func<DateTime>> _getTime =
        new ThreadLocal<Func<DateTime>>(() => () => DateTime.Now);

    /// <inheritdoc cref="DateTime.Today"/>
    public static DateTime Today
    {
        get { return _getTime.Value().Date; }
    }

    /// <inheritdoc cref="DateTime.Now"/>
    public static DateTime Now
    {
        get { return _getTime.Value(); }
    }

    /// <inheritdoc cref="DateTime.UtcNow"/>
    public static DateTime UtcNow
    {
        get { return _getTime.Value().ToUniversalTime(); }
    }

    /// <summary>
    /// Sets a fixed (deterministic) time for the current thread to return by <see cref="SystemClock"/>.
    /// </summary>
    public static void Set(DateTime time)
    {
        if (time.Kind != DateTimeKind.Local)
            time = time.ToLocalTime();

        _getTime.Value = () => time;
    }

    /// <summary>
    /// Resets <see cref="SystemClock"/> to return the current <see cref="DateTime.Now"/>.
    /// </summary>
    public static void Reset()
    {
        _getTime.Value = () => DateTime.Now;
    }
}

使用的例子:

[TestMethod]
public void Today()
{
    SystemClock.Set(new DateTime(2015, 4, 3));

    DateTime expectedDay = new DateTime(2015, 4, 2);
    DateTime yesterday = SystemClock.Today.AddDays(-1D);
    Assert.AreEqual(expectedDay, yesterday);

    SystemClock.Reset();
}

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;
    }
}

在使用ITimeProvider时，我们被迫将它作为一个特殊的共享项目，必须从其他项目中引用它。但这使得依赖关系的控制变得复杂。

我们在。net框架中搜索ITimeProvider。我们搜索了NuGet包，发现了一个不能使用DateTimeOffset的包。

所以我们提出了自己的解决方案，它只依赖于标准库的类型。我们正在使用Func<DateTimeOffset>的实例。

如何使用

public class ThingThatNeedsTimeProvider
{
    private readonly Func<DateTimeOffset> now;
    private int nextId;

    public ThingThatNeedsTimeProvider(Func<DateTimeOffset> now)
    {
        this.now = now;
        this.nextId = 1;
    }

    public (int Id, DateTimeOffset CreatedAt) MakeIllustratingTuple()
    {
        return (nextId++, now());
    }
}

如何注册

自发法克

builder.RegisterInstance<Func<DateTimeOffset>>(() => DateTimeOffset.Now);

(未来的编辑请在这里附上你的案例)。

如何进行单元测试

public void MakeIllustratingTuple_WhenCalled_FillsCreatedAt()
{
    DateTimeOffset expected = CreateRandomDateTimeOffset();
    DateTimeOffset StubNow() => expected;
    var thing = new ThingThatNeedsTimeProvider(StubNow);

    var (_, actual) = thing.MakeIllustratingTuple();

    Assert.AreEqual(expected, actual);
}

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

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;
        }
    }
}