你在它上面断言的东西叫做模拟对象。

其他帮助测试运行的东西都是存根。

这是一个让测试富有表现力的问题。如果我想让测试描述两个对象之间的关系，我就在Mock上设置期望。我存根返回值，如果我设置一个支持对象，让我在测试中有趣的行为。

根据Vladimir Khorikov的《单元测试原则、实践和模式》一书:

Mocks: help to emulate and examine outcoming interactions. These interactions are calls the SUT makes to its dependencies to change their state. In other words it helps to examine the interaction (behaviour) of SUT and its dependencies. mocks could be : Spy : created manually Mocks : created using framework Stubs: helps to emulate incoming interactions. These interactions are calls the SUT makes to its dependencies to get input data. IN other words it helps to test the data passed to SUT. It could be 3 types Fake: is usually implemented to replace a dependency that doesn’t yet exist. Dummy: is hard-coded value. Stubs: Fledged dependency that you configure to return different values for different scenarios.

存根——为方法调用提供预定义答案的对象。

Mock -一个你设定期望的对象。

假的——一个功能有限的对象(用于测试)，例如一个假的web服务。

Test Double是存根、mock和fake的总称。但非正式地，你会经常听到人们简单地称之为mock。

为了说明存根和模拟的用法，我还想包括一个基于Roy Osherove的“单元测试的艺术”的例子。

想象一下，我们有一个LogAnalyzer应用程序，它的唯一功能是打印日志。它不仅需要与web服务对话，而且如果web服务抛出错误，LogAnalyzer必须将错误记录到不同的外部依赖项，通过电子邮件发送给web服务管理员。

下面是我们想要在LogAnalyzer中测试的逻辑:

if(fileName.Length<8)
{
 try
  {
    service.LogError("Filename too short:" + fileName);
  }
 catch (Exception e)
  {
    email.SendEmail("a","subject",e.Message);
  }
}

当web服务抛出异常时，如何测试LogAnalyzer正确地调用电子邮件服务? 以下是我们面临的问题:

我们如何替换web服务? 我们如何模拟来自web服务的异常，以便我们可以 测试对电子邮件服务的调用? 我们如何知道电子邮件服务是否被正确调用 所有的吗?

我们可以通过使用web服务的存根来处理前两个问题。为了解决第三个问题，我们可以为电子邮件服务使用一个模拟对象。

A fake is a generic term that can be used to describe either a stub or a mock.In our test, we’ll have two fakes. One will be the email service mock, which we’ll use to verify that the correct parameters were sent to the email service. The other will be a stub that we’ll use to simulate an exception thrown from the web service. It’s a stub because we won’t be using the web service fake to verify the test result, only to make sure the test runs correctly. The email service is a mock because we’ll assert against it that it was called correctly.

[TestFixture]
public class LogAnalyzer2Tests
{
[Test]
 public void Analyze_WebServiceThrows_SendsEmail()
 {
   StubService stubService = new StubService();
   stubService.ToThrow= new Exception("fake exception");
   MockEmailService mockEmail = new MockEmailService();

   LogAnalyzer2 log = new LogAnalyzer2();
   log.Service = stubService
   log.Email=mockEmail;
   string tooShortFileName="abc.ext";
   log.Analyze(tooShortFileName);

   Assert.AreEqual("a",mockEmail.To); //MOCKING USED
   Assert.AreEqual("fake exception",mockEmail.Body); //MOCKING USED
   Assert.AreEqual("subject",mockEmail.Subject);
 }
}

它们都被称为Test Doubles，用于注入测试用例所需的依赖项。

存根: 它已经有一个预定义的行为来设置您的期望 例如，stub只返回API响应的成功案例

mock是更聪明的存根。您验证您的测试通过了它。 所以你可以让amock返回成功或失败成功取决于你的测试用例可以改变的条件。