java 模拟静态类

Mocking static class

提问by jerome

I have a method in a class that instantiate a static class instance and call operation on it.

我在一个类中有一个方法，它实例化一个静态类实例并对其调用操作。

public class SomeClass {
    public void someMethod() {
       MyClass.MyStaticClass myStaticClassInstance =
          new MyClass.MyStaticClass( arg1, arg2, arg3 );
       myStaticClassInstance.callSomeMethod();
    }
}

public class MyClass {

   public static class MyStaticClass {

      public MyStaticClass( Object arg1, Object arg2, Object arg3 ) {
      }

      public void callSomeMethod() {
      }
   }
}

How to mock static class instanciation, so that I could mock callSomeMethod()without going through the static class constructor ?

如何模拟静态类实例化，以便我可以在callSomeMethod()不通过静态类构造函数的情况下进行模拟？

采纳答案by Nicolas Filotto

You can do it with PowerMockby mocking instantiation of your static inner class. This can be done by preparing the class that will actually instantiate your static inner class so here it will be the class in which you have the method someMethod()defined.

您可以PowerMock通过模拟静态内部类的实例化来实现。这可以通过准备实际实例化静态内部类的类来完成，因此这里将是您someMethod()定义方法的类。

Assuming that someMethod()is defined into the class MyOtherClassand returns nothing, your test class would be something like this:

假设someMethod()定义到类中MyOtherClass并且不返回任何内容，您的测试类将是这样的：

@RunWith(PowerMockRunner.class) // The runner of PowerMock
@PrepareForTest(MyOtherClass.class) // the class to prepare
public class MyClassTest {

    @Test
    public void test() throws Exception {
        // The mock of your static inner class to return
        MyClass.MyStaticClass mock = Mockito.mock(MyClass.MyStaticClass.class);
        // Mock the call of callSomeMethod()
        PowerMockito.doAnswer(
            new Answer<Void>() {
                @Override
                public Void answer(final InvocationOnMock invocation) throws Throwable {
                    // Do something here as new implementation of callSomeMethod
                    System.out.println("My new Answer");
                    return null;
                }
            }
        ).when(mock).callSomeMethod();
        // Return your mock in case we instantiate MyClass.MyStaticClass in 
        // the prepared class with any arguments  
        PowerMockito.whenNew(MyClass.MyStaticClass.class)
            .withArguments(Matchers.any(), Matchers.any(), Matchers.any())
            .thenReturn(mock);

        // The code that will call someMethod
        MyOtherClass mc = new MyOtherClass();
        mc.someMethod();
    }
}

Assuming that my class MyClasslooks like this:

假设我的班级MyClass看起来像这样：

public class MyClass {

    public static class MyStaticClass {
        public MyStaticClass(Object arg1, Object arg2, Object arg3) {
            System.out.println("Called constructor");
        }

        public void callSomeMethod() {
            System.out.println("callSomeMethod");
        }
    }
}

And my class MyOtherClasslooks like this:

我的班级MyOtherClass看起来像这样：

public class MyOtherClass {
    public void someMethod() {
        MyClass.MyStaticClass myStaticClassInstance = new MyClass.MyStaticClass(
            new Object(), new Object(), new Object()
        );
        myStaticClassInstance.callSomeMethod();
    }
}

If I launch my test, I get as expected:

如果我启动我的测试，我会得到预期的结果：

My new Answer

Instead of what I should get by default:

而不是我默认应该得到的：

Called constructor
callSomeMethod

More details about how to constructions of new objects.

有关如何构造新对象的更多详细信息。

回答by iirekm

I wrote a simpler tool for mocking things that are normally 'non-mockable' at https://github.com/iirekm/misc/tree/master/ajmock

我在https://github.com/iirekm/misc/tree/master/ajmock写了一个更简单的工具来模拟通常“不可模拟”的东西

Your code can look like:

您的代码可能如下所示：

``` public class MyClassTest {

``` 公共类 MyClassTest {

@Test
public void test() throws Exception {
    MyClass.MyStaticClass mock = Mockito.mock(MyClass.MyStaticClass.class);
    when(() -> mock.callSomeMethod()).thenAnswer(() -> ...);

    when(() -> new MyClass.MyStaticClass(any(), any(), any())).thenReturn(mock);

    // The code that will call someMethod
    MyOtherClass mc = new MyOtherClass();
    mc.someMethod();
}

}

}

```

``