当我们无法将模拟对象传递给类的实例时，如何使用Mockito [英] How to use Mockito when we cannot pass a mock object to an instance of a class

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，我调用该方法以这种方式进行测试：

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类：

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;
    } 
}

现在我不能将我的模拟作为参数传递，所以我将如何测试我的方法？有人可以展示一个例子吗？

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，你试图用一个替代实现替换一个私有字段，这意味着你这违反了封装。你唯一的另一个选择是重新构建类或方法，使其更好地设计用于测试。

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'我在这里汇总他们（并添加我自己的几个）作为社区Wiki。 如果您有任何其他选择，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，或放宽字段的可见性。



• 创建依赖注入覆盖或静态方法接受DAO，并使公共实例方法委托给它。测试更灵活的方法。

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

• 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 */ }

添加构造函数重载或静态工厂方法，为了测试而替换私有字段。

为依赖注入。 （ Sotirios Delimanolis ， EJK ）

Add a constructor overload or static factory method that replaces private fields for the sake of testing.

Fully structure the class for dependency injection. (Sotirios Delimanolis, EJK)

请注意，如果您将测试放在同一个测试中，其中一些可以是封装专用的Java包（可能在一个单独的源代码树中）。在所有情况下，良好的名称和文档都有助于明确您的意图。

Note that some of these can be package-private for testing, if you put your tests in the same Java package (possibly in a separate source tree). In all cases, good names and documentation are helpful to make your intentions clear.

• 使用反射在类中设置私有字段。 （ kinbiko - 请参阅回答）


• 使用 PowerMockito 使用您选择的模拟替换 Dao 构造函数。 （ Dave Newton ）

• Use reflection to set private fields in the class. (kinbiko - see answer)
• Use PowerMockito to replace the Dao constructor with a mock of your choice. (Dave Newton)

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