在C#中,如何在单元测试时模拟/伪造/替换/存根基类?

更新:我改变了问题的措辞。以前,基类是否可以在运行时更改是一个“是/否”问题。

我可能在做不可能完成的任务,但我似乎已经接近了。我想扩展一个ASP.NET控件,并且我希望我的代码是可单元测试的。另外,我希望能够伪造真实标签的行为(即ID生成等),而真实标签在nUnit主机中是做不到的。

这里有一个工作示例,它对依赖于真实基类的内容和不依赖于真实基类的内容进行断言—在更现实的单元测试中,测试将同时依赖于这两个内容—即,现有的ID和一些自定义行为。

不管怎么说代码比我说得好:

public class LabelWrapper : Label //Runtime
//public class LabelWrapper : FakeLabel //Unit Test time
{
    private readonly LabelLogic logic= new LabelLogic();

    public override string Text
    {
        get
        {
            return logic.ProcessGetText(base.Text);
        }
        set
        {
            base.Text=logic.ProcessSetText(value);
        }
    }
}

//Ugh, now I have to test FakeLabelWrapper
public class FakeLabelWrapper : FakeLabel //Unit Test time
{
    private readonly LabelLogic logic= new LabelLogic();

    public override string Text
    {
        get
        {
            return logic.ProcessGetText(base.Text);
        }
        set
        {
            base.Text=logic.ProcessSetText(value);
        }
    }
}

[TestFixture]
public class UnitTest
{
    [Test]
    public void Test()
    {
        //Wish this was LabelWrapper label = new LabelWrapper(new FakeBase())
        LabelWrapper label = new LabelWrapper();
        //FakeLabelWrapper label = new FakeLabelWrapper();
        label.Text = "ToUpper";
        Assert.AreEqual("TOUPPER",label.Text);
        StringWriter stringWriter = new StringWriter();
        HtmlTextWriter writer = new HtmlTextWriter(stringWriter);
        label.RenderControl(writer);
        Assert.AreEqual(1,label.ID);
        Assert.AreEqual("<span>TOUPPER</span>", stringWriter.ToString());
    }
}

public class FakeLabel
{
    virtual public string Text { get; set; }
    public void RenderControl(TextWriter writer)
    {
        writer.Write("<span>" + Text + "</span>");
    }
}

//System Under Test
internal class LabelLogic
{
    internal string ProcessGetText(string value)
    {
        return value.ToUpper();
    }

    internal string ProcessSetText(string value)
    {
        return value.ToUpper();
    }
}