通常一个典型的asp.net控件至少会用ViewState存储一些属性,以便于在页面postback后不用重新设置。在这篇文章里我将介绍如何为控件写单元测试，以确保一个属性被正确的保存在ViewState里。

为了演示，我写了一个简单的控件。

namespace Eilon.Sample.Controls {
using System;
using System.Web.UI;
public class NewLabel : Control {
public string Text {
get {
string s = ViewState["Text"] as string;
return s ?? String.Empty;
}
set {
ViewState["Text"] = value;
}
}
protected override void Render(HtmlTextWriter writer) {
writer.Write(Text);
}
}
}

这个控件只是简单的将它唯一的属性Text输出。

好的，让我们写一个简单的单元测试，以确保这个控件正确的工作。

namespace Eilon.Sample.Controls.Test {
using System;
using System.IO;
using System.Web.UI;
using Microsoft.VisualStudio.TestTools.UnitTesting;
[TestClass]
public class NewLabelTest {
[TestMethod]
public void TextReturnsEmptyStringDefault() {
NewLabel label = new NewLabel();
Assert.AreEqual<string>(String.Empty, label.Text,

"Default text should be empty string (not null)");
}
[TestMethod]
public void GetSetText() {
const string value = "Some Text";
NewLabel label = new NewLabel();
label.Text = value;
Assert.AreEqual<string>(value, label.Text,

"Property value isn't the same as what we set");
}
[TestMethod]
public void RenderEmpty() {
NewLabel label = new NewLabel();
Assert.AreEqual<string>(String.Empty, GetRenderedText(label),

"Shouldn't have rendered anything");
}
[TestMethod]
public void RenderWithText() {
const string value = "Some Text";
NewLabel label = new NewLabel();
label.Text = value;
Assert.AreEqual<string>(value, GetRenderedText(label),

"Should have rendered the text");
}
private static string GetRenderedText(Control c) {
HtmlTextWriter writer = new HtmlTextWriter(new StringWriter());
c.RenderControl(writer);
return writer.InnerWriter.ToString();
}
}
}

看上去我们已经覆盖了100%的代码，是这样吗？事实上我们根本不能保证这个控件的属性已经被正确的存储到ViewState里了。可是我们知道与ViewState有关的函数都是protected的，并不能从外部访问。解决这个问题，可以有很多办法，这里我们写一个internal interface，

// Interface to expose protected methods from
// the Control class to our unit test
internal interface IControl {
void LoadViewState(object savedState);
object SaveViewState();
void TrackViewState();
}
然后让我们的控件去实现它：

#region IControl Members
void IControl.LoadViewState(object savedState) {
LoadViewState(savedState);
}
object IControl.SaveViewState() {
return SaveViewState();
}
void IControl.TrackViewState() {
TrackViewState();
}
#endregion

现在就可以测试ViewState了：

[TestMethod]
public void TextSavedInViewState() {
// Create the control, start tracking viewstate,
// then set a new Text value
const string firstValue = "Some Text";
const string secondValue = "ViewState Text";
NewLabel label = new NewLabel();
label.Text = firstValue;
((IControl)label).TrackViewState();
label.Text = secondValue;
// Save the control's state
object viewState = ((IControl)label).SaveViewState();
// Create a new control instance and load the state
// back into it, overriding any existing values
NewLabel newLabel = new NewLabel();
label.Text = firstValue;
((IControl)newLabel).LoadViewState(viewState);
Assert.AreEqual<string>(secondValue, newLabel.Text,
"Value restored from viewstate does not match the original value we set");
}

这里注意一点，我们的接口是internal的，为了让测试用例可以访问它，需要添加

using System.Runtime.CompilerServices;
[assembly: InternalsVisibleTo("MyControlLibrary.Test")]