JUnit使用Mockito测试异步方法

Question

我使用Spring Framework（版本5.0.5.RELEASE）在Java 1.8类中实现了一个异步方法：

public class ClassToBeTested {
    @Autowired
    private MyComponent myComponent;

    @Async
    public void doStuff(List<MyClass> myObjects) {
        CompletableFuture<MyResponseObject>[] futureList = new CompletableFuture[myObjects.size()];
        int count = 0;

        for (MyClass myObject : myObjects) {
            futureList[count] = myComponent.doOtherStuff(myObject);
            count++;
        }

        // Wait until all doOtherStuff() calls have been completed
        CompletableFuture.allOf(futureList).join();

        ... other stuff ...
    }
}

我正试图用JUnit和Mockito来测试这个课程。 我已经设置如下，目的是模拟doStuff（）方法对组件的调用：

@MockBean
private MyComponent myComponentAsAMock;

@InjectMocks
@Autowired
private ClassToBeTested classToBeTested;

@Test
public void myTest() throws Exception {
    // Create object to return when myComponent.doOtherStuff() is called.
    CompletableFuture<MyResponseObject> completableFuture = new CompletableFuture<MyResponseObject>();
    ... populate an instance of MyResponseObject ...
    completableFuture.complete(myResponseObject);

    // Return object when myComponent.doOtherStuff() is called.
    Mockito.when(
        myComponentAsAMock.doOtherStuff(ArgumentMatchers.any(MyClass.class)))
        .thenReturn(completableFuture);

    // Test.
    List<MyClass> myObjects = new ArrayList<MyClass>();
    MyClass myObject = new MyClass();
    myobjects.add(myObject);
    classToBeTested.doStuff(myObjects);
}

虽然我在Eclipse中单独运行单元测试似乎是成功的，但是在整个项目中进行Maven构建时我注意到抛出了NullPointerExceptions：

[ThreadExecutor2] .a.i.SimpleAsyncUncaughtExceptionHandler : Unexpected error occurred invoking async method 'public void package.ClassToBeTested.doStuff(java.util.List)'.

java.lang.NullPointerException: null
at java.util.concurrent.CompletableFuture.andTree(CompletableFuture.java:1306) ~[na:1.8.0_131]
at java.util.concurrent.CompletableFuture.allOf(CompletableFuture.java:2225) ~[na:1.8.0_131]
at package.ClassToBeTested.doStuff(ClassToBeTested.java:75) ~[classes/:na]

在这行ClassToBeTested.java上引发了错误：

CompletableFuture.allOf(completedFutureList).join();

在测试完成后， 看起来异常消息正在Maven构建输出中显示（正在运行其他测试，其输出发生在显示错误消息之前），所以我猜测它与事实有关对doStuff（）的调用是异步的。

任何援助将不胜感激。

Answer 1

解决方案是在Mockito验证步骤中添加超时和检查以确保模拟组件的方法被调用适当的次数：

    Mockito.verify(myComponentAsAMock, Mockito.timeout(1000).times(1)).doOtherStuff(ArgumentMatchers.any(MyClass.class));