艾伟：为WPF项目创建单元测试

可能你已发现一个问题,我们无法使用VS对WPF项目创建单元测试(VS2005不行,VS2008我没试过,但据说也不行),这让人很郁闷,这里将介绍如何使用NUnit来对WPF项目创建单元测试并解决其中的难题(但利用NUnit来对WPF创建单元测试时并不会像针对.Net2.0一样容易，可能会出现一些小问题).

1,对普通类（非WPF UI组件）进行测试：
 这和在.Net2.0中使用NUnit进行测试时一样，不会出现任何问题，参考下面的代码:

    [TestFixture]
    public class ClassTest
    {
        [Test]
        public void TestRun()
        {
            ClassLibrary1.Class1 obj = new ClassLibrary1.Class1();

            double expected = 9;
            double result = obj.GetSomeValue(3);

            Assert.AreEqual(expected, result);
        }
     }

2,对WPF UI组件进行测试
 使用NUnit对WPF UI组件（比如MyWindow，MyUserControl）进行测试的时候，NUnit会报如下异常：“The calling thread must be STA, because many UI components require this”。
下面是错误的测试代码:

[TestFixture]
    public class ClassTest
    {
        [Test]
        public void TestRun()
        {
            WindowsApplication1.Window1 obj = new WindowsApplication1.Window1();

            double expected = 9;
            double result = obj.GetSomeValue(3);

            Assert.AreEqual(expected, result);
        }
     }

为了让调用线程为STA，我们可以编写一个辅助类CrossThreadTestRunner:

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;
using System.Security.Permissions;
using System.Reflection;

namespace TestUnit
{
    public class CrossThreadTestRunner
    {
        private Exception lastException;

        public void RunInMTA(ThreadStart userDelegate)
        {
            Run(userDelegate, ApartmentState.MTA);
        }

        public void RunInSTA(ThreadStart userDelegate)
        {
            Run(userDelegate, ApartmentState.STA);
        }

        private void Run(ThreadStart userDelegate, ApartmentState apartmentState)
        {
            lastException = null;

            Thread thread = new Thread(
              delegate()
              {
                  try
                  {
                      userDelegate.Invoke();
                  }
                  catch (Exception e)
                  {
                      lastException = e;
                  }
              });
            thread.SetApartmentState(apartmentState);

            thread.Start();
            thread.Join();

            if (ExceptionWasThrown())
                ThrowExceptionPreservingStack(lastException);
        }

        private bool ExceptionWasThrown()
        {
            return lastException != null;
        }

        [ReflectionPermission(SecurityAction.Demand)]
        private static void ThrowExceptionPreservingStack(Exception exception)
        {
            FieldInfo remoteStackTraceString = typeof(Exception).GetField(
              "_remoteStackTraceString",
              BindingFlags.Instance | BindingFlags.NonPublic);
            remoteStackTraceString.SetValue(exception, exception.StackTrace + Environment.NewLine);
            throw exception;
        }
    }
}

并编写正确的测试代码：

    [TestFixture]
    public class ClassTest
    {
        [Test]
        public void TestRun()
        {
            
            CrossThreadTestRunner runner = new CrossThreadTestRunner();
            runner.RunInSTA(
              delegate
              {
                  Console.WriteLine(Thread.CurrentThread.GetApartmentState());

                  WindowsApplication1.Window1 obj = new WindowsApplication1.Window1();

                  double expected = 9;
                  double result = obj.GetSomeValue(3);
                  Assert.AreEqual(expected, result);
              });   

        }
  }

另外，使用NUnit时，您需要添加对nunit.framework.dll的引用，并对测试类添加[TestFixture]属性标记以及对测试方法添加[Test]属性标记，然后将生成的程序集用nunit.exe打开就可以了，关于NUnit的具体用法您可以参考其官方文档。