什麼時候應該斷言SUT的行爲？

Question

考慮以下的單元測試：

[Test] 
public void Success() 
{ 
    var userID = 5; 
    var user = new User(); 
    var dataAccess = new Mock<IDataAccess>(); 
    dataAccess.Setup(x => x.GetUser(userID)).Returns(user).Verifiable(); 
    var sut = new UserController(dataAccess.Object); 

    var returnedUser = sut.GetUser(userID); 

    Assert.AreSame(user, returnedUser); 
    dataAccess.Verify(x => x.GetUser(userID), Times.Once()); 
} 

最近讀數已建議我應該只使用模擬，以提供用戶和應該有一個單一的斷言（所述AreSame之一）。顯然理想的單元測試不應該擔心驗證sut的行爲。

更多類似這樣的：

[Test] 
public void Success() 
{ 
    var userID = 5; 
    var user = new User(); 
    var dataAccess = new Mock<IDataAccess>(); 
    dataAccess.Setup(x => x.GetUser(userID)).Returns(user); 
    var sut = new UserController(dataAccess.Object); 

    var returnedUser = sut.GetUser(userID); 

    Assert.AreSame(user, returnedUser); 
} 

這是簡化的測試更好？單元測試應該斷言它們所調用的方法的行爲還是僅僅是結果？

Answer 1

一個基本思想是只有一個斷言在測試。所以也許你應該在這裏考慮兩個測試。第一個基於價值的測試很重要。第二次互動測試可能不適合這種情況。根據Roy Osherove的說法：'在調用另一個對象時使用交互測試是特定工作單元的最終結果。'

實施例：

namespace Tests 
{ 
    [TestClass] 
    public class UserControllerTest 
    { 
     [TestMethod] 
     public void GetUser_WhenCalled_ReturnsUserSameAsDataAccess() 
     { 
      // Arrange 
      const int userID = 5; 
      User expectedUser = new User(); 

      Mock<IDataAccess> dataAccessStub = new Mock<IDataAccess>(); 
      dataAccessStub.Setup(x => x.GetUser(userID)).Returns(expectedUser); 
      UserController controller = new UserController(dataAccessStub.Object); 

      // Act 
      User actualUser = controller.GetUser(userID); 

      // Assert 
      Assert.AreSame(expectedUser, actualUser); 
     } 

     [TestMethod] 
     public void GetUser_WhenCalled_GetUserOnDataAccessIsCalledOnce() 
     { 
      // Arrange 
      const int userID = 5; 
      const int getUserCallsCountExpected = 1; 
      int getUserCallsCount = 0; 

      Mock<IDataAccess> dataAccessMock = new Mock<IDataAccess>(); 
      dataAccessMock.Setup(x => x.GetUser(userID)).Callback(() => getUserCallsCount++); 
      UserController controller = new UserController(dataAccessMock.Object); 

      // Act 
      controller.GetUser(userID); 

      // Assert 
      Assert.AreEqual(getUserCallsCountExpected, getUserCallsCount); 
     } 
    } 
} 

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