為Asp.net控制項寫單元測試(ViewState)

 

通常一個典型的asp.net控制項至少會用ViewState儲存一些屬性,以便於在頁面postback後不用重新設定。在這篇文章裡我將介紹如何為控制項寫單元測試，以確保一個屬性被正確的儲存在ViewState裡。

為了示範，我寫了一個簡單的控制項。

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);
}
}
}

這個控制項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，以確保這個控制項正確的工作。

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制項的屬性已經被正確的儲存到ViewState裡了。可是我們知道與ViewState有關的函數都是protected的，並不能從外部存取。解決這個問題，可以有很多辦法，這裡我們寫一個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();
}
然後讓我們的控制項去實現它：

#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;
((IControl)newLabel).LoadViewState(viewState);
Assert.AreEqual<string>(secondValue, newLabel.Text,
"Value restored from viewstate does not match the original value we set");
}

這裡注意一點，我們的介面是internal的，為了讓測試案例可以訪問它，需要添加

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