当我们无法将模拟对象传递给类的实例时如何使用 Mockito

问题描述

假设我有这样的课程:

public class MyClass {

    Dao dao;

    public String myMethod(Dao d) {

        dao = d;

        String result = dao.query();

        return result;
    } 
}

我想用 mockito 测试它.所以我创建了一个模拟对象并以这种方式调用该方法进行测试:

I want to test it with mockito. So I create a mock object and I call the method to test in that way:

Dao mock = Mockito.mock(Dao.class);

Mockito.when(mock.myMethod()).thenReturn("ok");

new MyClass().myMethod(mock);

但是，假设我有一个这样的课程:

But, suppose instead I have a class like that:

public class MyClass {

    Dao dao = new Dao();

    public String myMethod() {

        String result = dao.query();

        return result;
    } 
}

现在我无法将我的模拟作为参数传递，那么我将如何测试我的方法?有人可以举个例子吗?

Now I cannot pass my mock as an argument, so how I gonna test my method? Can someone show an example?

推荐答案

从根本上说，您试图用替代实现替换私有字段，这意味着您违反了封装.您唯一的其他选择是重组类或方法，使其更适合测试.

Fundamentally, you're trying to replace a private field with an alternative implementation, which means you'd violate encapsulation. Your only other option is to restructure the class or method, to make it better-designed for testing.

评论中有很多简短的答案，所以我在这里将它们汇总(并添加我自己的几个)作为社区 Wiki.如果您有任何替代方案，请随时在此处添加.

There are a lot of short answers in the comments, so I'm aggregating them here (and adding a couple of my own) as Community Wiki. If you have any alternatives, please feel free to add them here.

• 为相关字段创建一个 setter，或放宽该字段的可见性.

• Create a setter for the field in question, or relax the field's visibility.

创建一个采用 DAO 的依赖注入覆盖或静态方法，并将公共实例方法委托给它.改为测试更灵活的方法.

Create a dependency-injecting override or static method that takes a DAO, and make the public instance method delegate to it. Test the more-flexible method instead.

public String myMethod() { return myMethod(dao); }
String myMethod(Dao dao) { /* real implementation here */ }