测试-如何创建Mock对象 [英] Testing - how to create Mock object

问题描述

我只是想知道如何创建Mock对象来测试如下代码:

I am just wondering how can I create Mock object to test code like:

public class MyTest
{
  private A a;
  public MyTest()
  {
     a=new A(100,101);
  }
}

?

谢谢

推荐答案

直接使用new实例化对象的代码使测试变得困难.通过使用工厂模式，您可以将对象的创建移到要测试的代码之外.这为您提供了一个放置模拟对象和/或模拟工厂的地方.

Code that instantiates objects using new directly makes testing difficult. By using the Factory pattern you move the creation of the object outside of the code to be tested. This gives you a place to inject a mock object and/or mock factory.

请注意，您选择MyTest作为要测试的类有点不幸，因为名称暗示它本身就是测试本身.我将其更改为MyClass.另外，可以通过传入A的实例来轻松替换在构造函数中创建对象的过程，因此我将创建的内容移至以后将被调用的方法.

Note that your choice of MyTest as the class to be tested is a bit unfortunate as the name implies that it is the test itself. I'll change it to MyClass. Also, creating the object in the constructor could easily be replaced by passing in an instance of A so I'll move the creation to a method that would be called later.

public interface AFactory
{
    public A create(int x, int y);
}

public class MyClass
{
    private final AFactory aFactory;

    public MyClass(AFactory aFactory) {
        this.aFactory = aFactory;
    }

    public void doSomething() {
        A a = aFactory.create(100, 101);
        // do something with the A ...
    }
}

现在，您可以在测试中传递一个模拟工厂，该工厂将创建您选择的模拟A或A.让我们使用Mockito创建模拟工厂.

Now you can pass in a mock factory in the test that will create a mock A or an A of your choosing. Let's use Mockito to create the mock factory.

public class MyClassTest
{
    @Test
    public void doSomething() {
        A a = mock(A.class);
        // set expectations for A ...
        AFactory aFactory = mock(AFactory.class);
        when(aFactory.create(100, 101)).thenReturn(a);
        MyClass fixture = new MyClass(aFactory);
        fixture.doSomething();
        // make assertions ...
    }
}

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