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?
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
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();
}
其他回答
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)
{
}
}
为系统添加一个假程序集(右键单击System reference=>添加假程序集)。
并在测试方法中写入:
using (ShimsContext.Create())
{
System.Fakes.ShimDateTime.NowGet = () => new DateTime(2014, 3, 10);
MethodThatUsesDateTimeNow();
}
模拟对象。
一个模拟DateTime,返回适合您的测试的Now。
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
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();
}