通常一個典型的asp.net控件至少會用ViewState存儲一些屬性,以便于在頁面postback后不用重新設置。在這篇文章里，北京北大青鳥校區將介紹如何為控件寫單元測試，以確保一個屬性被正確的保存在ViewState里。
為了演示，北京北大青鳥校區老師先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。
下面，北京北大青鳥校區老師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.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(value, label.Text,Property value isn't the same as what we set);}[TestMethod]public void RenderEmpty() {NewLabel label = new NewLabel();Assert.AreEqual(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(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。可是我們知道與ViewState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 testinternal interface IControl {void LoadViewState(object savedState);object SaveViewState();void TrackViewState();}
然后讓我們的控件去實現它：
#region IControl Membersvoid 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 valueconst 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 stateobject viewState = ((IControl)label).SaveViewState();// Create a new control instance and load the state// back into it, overriding any existing valuesNewLabel newLabel = new NewLabel();label.Text = firstValue;((IControl)newLabel).LoadViewState(viewState);Assert.AreEqual(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)]
文章來源：北京北大青鳥校區學術部
