David Ko的學習之旅

利用Stub來打破關連性 (2)

Source: The art of unit testing with examples in .NET, Roy Osherove
http://www.amazon.com/Art-Unit-Testing-Examples-Net/dp/1933988274/ref=sr_1_1?ie=UTF8&s=books&qid=1267086529&sr=1-1
Chapter 3 Using stubs to break dependencies

之前用constructor的方法來傳入stub object, 這樣的作法有什麼問題嗎?

有經驗的人一定會想到, 若是有多個stub object, 或是可能之後要動態增加stub時, 這樣的作法不就要常常改constructor, 因此作者提出另外一個作法: 利用property來設定stub.

方法 2.

public class LogAnalyzer {
  private IExtensionManager manager;
 
  // 設定指向真的File Extension Manager
  public LogAnalyzer() {
    manager = new FileExtensionManager();
  }
 
  // 隨時可以更改 Extension Manager 的內容
  public IExtensionManager ExtendsionManager {
    get { return manager; }
    set { manager = value;}
  }
   
  public bool IsValidLogFileName(string fileName) {
    return manager.IsValid(fileName);
  }
}

[TestFixture]
public class LogAnnalyzerTests {
 
  [Test]
  public void IsValidFileName_NameShorterThan6() {
   
    // 設定stub的內容
    StubExtensionManager myFakeManager =
      new StubExtensionManager();
    myFakeManager.ShouldExtensionBeValid = true;
   
    LogAnalyzer log = new LogAnalyzer();
   
    // 將stub object傳給受測的object
    log.ExtensionManager = myFakeManager;
   
    // 進行測試
    bool result = log.IsValidLogFileName( "short.ext" );
   
    // 檢查測試結果
    Assert.IsFalse( result, "File name with less than 5 chars should have failed the method." );
  }
 
  // File Extension Manager的stub 
  internal class StubExtensionManager : IExtensionManager {
    public bool ShouldExtensionBeValid;
   
    public bool IsValid(string fileName) {
      //實作僅供測試使用的功能
      return ShouldExtensionBeValid;
    }
  }
}