为了帮助进行单元测试,我们将DateTime类包装在委托中,以便可以在单元测试中覆盖DateTime.Now.

public static class SystemTime
{
    #region Static Fields

    public static Func<DateTime> Now = () => DateTime.Now;

    #endregion
}

这是在xunit单元测试中使用它的示例：

[Fact]
public void it_should_update_the_last_accessed_timestamp_on_an_entry()
{
    // Arrange
    var service = this.CreateClassUnderTest();

    var expectedTimestamp = SystemTime.Now();
    SystemTime.Now = () => expectedTimestamp;

    // Act
    service.UpdateLastAccessedTimestamp(this._testEntry); 

    // Assert
    Assert.Equal(expectedTimestamp, this._testEntry.LastAccessedOn);
}   

该测试在本地运行良好,但是由于Assert语句中的日期时间不同,因此在我们的构建服务器上失败了.

考虑到DateTime是通过上述委托包装器模拟的,因此我很难思考为什么它会失败的原因.我已经验证了UpdateLastAccessedTimestamp方法的实现没有问题,并且在本地运行时该测试通过了.

不幸的是,我无法在构建服务器上对其进行调试.有什么想法为什么它只有在构建服务器上运行时才会失败？

请注意,UpdateLastAccessedTimestamp的实现如下：

public void UpdateLastAccessedTimestamp(Entry entry)
{
    entry.LastAccessedOn = SystemTime.Now();
    this._unitOfWork.Entries.Update(entry);
    this._unitOfWork.Save();
}

Entry类只是一个简单的POCO类,它具有许多字段,包括LastAccessedOn字段：

public class Entry
{
   public DateTime LastAccessedOn { get; set; }

   //other fields that have left out to keep the example concise
}

解决方法:

您的问题可能是由于使用静态SystemTime进行了多个单元测试.例如,如果您要进行以下操作：

单元测试1

[Fact]
public void it_should_update_the_last_accessed_timestamp_on_an_entry()
{
    // Arrange
    var service = this.CreateClassUnderTest();

    var expectedTimestamp = SystemTime.Now();
    SystemTime.Now = () => expectedTimestamp;

    // Act
    service.UpdateLastAccessedTimestamp(this._testEntry); 

    // Assert
    Assert.Equal(expectedTimestamp, this._testEntry.LastAccessedOn);
}   

public void UpdateLastAccessedTimestamp(Entry entry)
{
    entry.LastAccessedOn = SystemTime.Now();
    this._unitOfWork.Entries.Update(entry);
    this._unitOfWork.Save();
}

单元测试2

[Fact]
public void do_something_different
{
    SystemTime.Now = () => DateTime.Now;
}

因此,假设单元测试2(全部)在单元测试1的两行之间触发：

SystemTime.Now = () => expectedTimestamp;

// Unit test 2 starts execution here

// Act
service.UpdateLastAccessedTimestamp(this._testEntry); 

如果发生这种情况,那么您的UpdateLastAccessedTimestamp将(不必)具有您在SystemTime上设置的预期DateTime值.Now=()=> ExpectedTimestamp ;,因为另一个测试已经覆盖了您从单元测试1中提供的功能.

这就是为什么我认为您最好将DateTime作为参数传递,或者使用可注入的datetime更好：

/// <summary>
/// Injectable DateTime interface, should be used to ensure date specific logic is more testable
/// </summary>
public interface IDateTime
{
    /// <summary>
    /// Current Data time
    /// </summary>
    DateTime Now { get; }
}

/// <summary>
/// DateTime.Now - use as concrete implementation
/// </summary>
public class SystemDateTime : IDateTime
{
    /// <summary>
    /// DateTime.Now
    /// </summary>
    public DateTime Now { get { return DateTime.Now; } }
}

/// <summary>
/// DateTime - used to unit testing functionality around DateTime.Now (externalizes dependency on DateTime.Now
/// </summary>
public class MockSystemDateTime : IDateTime
{
    private readonly DateTime MockedDateTime;

    /// <summary>
    /// Take in mocked DateTime for use in testing
    /// </summary>
    /// <param name="mockedDateTime"></param>
    public MockSystemDateTime(DateTime mockedDateTime)
    {
        this.MockedDateTime = mockedDateTime;
    }

    /// <summary>
    /// DateTime passed from constructor
    /// </summary>
    public DateTime Now { get { return MockedDateTime; } }
}

在这种情况下,您的服务类可能会发生如下变化：

public class Service
{
    public Service() { }

    public void UpdateLastAccessedTimestamp(Entry entry)
    {
        entry.LastAccessedOn = SystemTime.Now();
        this._unitOfWork.Entries.Update(entry);
        this._unitOfWork.Save();
    }
}

对此：

    public class Service
    {

        private readonly IDateTime _iDateTime;

        public Service(IDateTime iDateTime)
        {
            if (iDateTime == null)
                throw new ArgumentNullException(nameof(iDateTime));
            // or you could new up the concrete implementation of SystemDateTime if not provided

            _iDateTime = iDateTime;
        }

        public void UpdateLastAccessedTimestamp(Entry entry)
        {
            entry.LastAccessedOn = _iDateTime.Now;
            this._unitOfWork.Entries.Update(entry);
            this._unitOfWork.Save();
        }           
    }

对于服务的实际实现,您可以像(或使用IOC容器)进行更新：

Service service = new Service(new SystemDateTime());

为了进行测试,您可以使用模拟框架,也可以使用Mock类：

Service service = new Service(new MockDateTime(new DateTime(2000, 1, 1)));

您的单元测试可能变为：

[Fact]
public void it_should_update_the_last_accessed_timestamp_on_an_entry()
{
    // Arrange
    MockDateTime mockDateTime = new MockDateTime(new DateTime 2000, 1, 1);
    var service = this.CreateClassUnderTest(mockDateTime);

    // Act
    service.UpdateLastAccessedTimestamp(this._testEntry); 

    // Assert
    Assert.Equal(mockDateTime.Now, this._testEntry.LastAccessedOn);
}