java - JUnit 使用 Mockito 测试异步方法

Question

我已经使用 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 ...
    }
}

我正在尝试使用 JUnit 和 Mockito 测试该类。我已将其设置如下，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);
}

虽然当我在 Eclipse 中单独运行单元测试时它似乎是成功的，但是对整个项目进行 Maven 构建时我注意到 NullPointerExceptions 被抛出:

[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 ClassToBeTested.java 的这一行上引发了错误:

CompletableFuture.allOf(completedFutureList).join();

它看起来在测试完成后异常消息显示在 Maven 构建输出中(还有其他正在运行的测试，其输出发生在显示错误消息之前)，所以我我猜这与对 doStuff() 的调用是异步的这一事实有关。

如有任何帮助，我们将不胜感激。

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已被调用适当的次数:

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