為了演示，我寫了一個簡單的控件。
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); } } } 這個控件只是簡單的將它唯一的屬性Text輸出。
好的，讓我們寫一個簡單的單元測試，以確保這個控件正確的工作。
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(); } } } 看上去我們已經覆蓋了100%的代碼，是這樣嗎？事實上我們根本不能保證這個控件的屬性已經被正確的存儲到ViewState里了�？墒俏覀冎琅cViewState有關的函數都是protected的，并不能從外部訪問。解決這個問題，可以有很多辦法，這里我們寫一個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(); } 然后讓我們的控件去實現它：
#region IControl Members void IControl.LoadViewState(object savedState) { LoadViewState(savedState); } object IControl.SaveViewState() { return SaveViewState(); } void IControl.TrackViewState() { TrackViewState(); } #endregion 現在就可以測試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; <string>(secondValue, newLabel.Text, "Value restored from viewstate does not match the original value we set"); } 這里注意一點，我們的接口是internal的，為了讓測試用例可以訪問它，需要添加
using System.Runtime.CompilerServices; [assembly: InternalsVisibleTo("MyControlLibrary.Test")]
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