Mock object framework (1) @ David Ko的學習之旅

Mock object framework (1)

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 5 Isolation (mock object) framework

由前一個章節可以知道, 若是要自己撰寫stub或是mock, 會很花時間. 若是受測程式的interface很複雜, method很多, parameter很多, 都會使難度變高.

所以若是有個mock object framework來幫助我們處理這些事情, 將會大大解省開發的代價. 在這裡作者要和我們推薦的是Rhino Mock, 你可以在http://ayende.com中下載它們

這裡我們先來看若是沒有用Rhino Mock, 那測試程式會怎麼寫
// 受測程式
public class LogAnalyzer {
private IWebService service;

public LogAnalyzer(IWebService service) {
    this.service = service;
}

public void Analyze(string filename) {
    if (filename.Length < 8 ) {
      service.LogError("Filename too short:" + filename );
    }
}
}

// 自己實作mock object
public class ManualMockService: IWebService {
public string LastError;

public void LogError(string message) {
LastError = message;
}
}

[TestFixture]
public class LogAnalyzerTests {
[Test]
public void Analyze_TooShortFileName() {

    ManualMockService mockService = new ManualMockService();

    LogAnalyzer log = new LogAnalyzer( mockService);

    string tooShortFileName = "abc.ext";
    log.Analyze(tooShortFileName);

    Assert.AreEqual("Filename too short: abc.ext", mockService.LastError );
}
}

改成使用Rhino Mocks會變成這樣:
[Test]
public void Analyze_TooShortFileName() {
// create dynamic mock object
MockRepository mocks = new MockRepository();
IWebService simulatedServoce = mocks.StrictMock<IWebService>();

// 在這裡你要先紀錄哪個method要被叫
// 會傳入哪些資料
// 以供之後比對是否真實情況是這樣使用
using(mocks.Record()) {
simulatedServoce.LogError("Filename too short: abc.ext");
}

// invokes LogAnalyzer
LogAnalyzer log = new LogAnalyzer( simulatedServoce);
string tooShortFileName = "abc.ext";
log.Analyze(tooShortFileName);

// 比對受測程式是否以預期的方式呼叫
mocks.Verify(simulatedServoce);
}