问题

我正在使用Mockito测试以下方法：

```java
protected void produceProducedFieldValue(Target target) throws ValueProducerCreationException {
    String mappedValue = (String) valueProducerFactory.createValueProducer("IdProducer", Collections.emptyList()).get();
    target.setProducedField(mappedValue);
}

这是我的测试：

@Test
public void TestProducingProducedFieldValue() throws ValueProducerCreationException {
    Target mockedTarget = Mockito.mock(Target.class);
    ValueProducerFactory valueProducerFactory = Mockito.mock(ValueProducerFactory.class);
    List<Object> creationParameters = new ArrayList<>();

    String mappedValue = "SomeString";

    Mockito.when(valueProducerFactory.createValueProducer("IdProducer", Collections.emptyList()).get()).thenReturn(mappedValue);
    SourceToTargetMapper sttm = new SourceToTargetMapper(targetModelObjectFactory, mappingOperatorFactory, mapperFactory, valueProducerFactory);
    sttm.produceProducedFieldValue(mockedTarget);
    Mockito.verify(mockedTarget, Mockito.times(1)).setProducedField(Mockito.any());
}

但是我一直在这一行中收到NullPointerException：

Mockito.when(valueProducerFactory.createValueProducer("IdProducer", Collections.emptyList()).get()).thenReturn(mappedValue);

ValueProducerFactory是一个接口

而createValueProducer方法的签名如下：

public interface ValueProducerFactory {

    <T> Supplier<T> createValueProducer(String producerName, List<Object> creationParameters) throws ValueProducerCreationException;

}

我有一个名为CachingValueProducerFactory的类，它实现了这个接口

@Override
public <T> Supplier<T> createValueProducer(String producerName, List<Object> creationParameters) throws ValueProducerCreationException {
    Map<List<Object>, Supplier<?>> parametersToOperatorsMap = producersCache.computeIfAbsent(producerName, s -> new HashMap<>());

    List<Object> key = Optional.ofNullable(creationParameters).orElse(Collections.emptyList());

    if (!parametersToOperatorsMap.containsKey(key)) {
        parametersToOperatorsMap.put(key, nestedProducersFactory.createValueProducer(producerName, creationParameters));
    }

    return (Supplier<T>) parametersToOperatorsMap.get(key);
}

似乎在测试中使用Collections.emptyList()是问题所在，但我没有看到其他解决方案。

<details>
<summary>英文:</summary>

I&#39;m using Mockito to test the following method:

```java
  protected void produceProducedFieldValue(Target target) throws ValueProducerCreationException {
    String mappedValue = (String) valueProducerFactory.createValueProducer(&quot;IdProducer&quot;, Collections.emptyList()).get();
    target.setProducedField(mappedValue);
  }

Here is my test:

     @Test
    public void TestProducingProducedFieldValue() throws ValueProducerCreationException {

        Target mockedTarget = Mockito.mock(Target.class);
        ValueProducerFactory valueProducerFactory = Mockito.mock(ValueProducerFactory.class);
        List<Object> creationParameters = new ArrayList<>();

        String mappedValue= "SomeString";

        Mockito.when(valueProducerFactory.createValueProducer("IdProducer", Collections.emptyList()).get()).thenReturn(mappedValue);
        SourceToTargetMapper sttm = new SourceToTargetMapper(targetModelObjectFactory,mappingOperatorFactory,mapperFactory,valueProducerFactory);
        sttm.produceProducedFieldValue(mockedTarget);
        Mockito.verify(mockedTarget, Mockito.times(1)).setProducedField(Mockito.any());
    }

But I keep getting NullPointerExeption for this line:

    Mockito.when(valueProducerFactory.createValueProducer("IdProducer", Collections.emptyList()).get()).thenReturn(mappedValue);

ValueProducerFactory is an Interface

and the createValueProducer method signature is as follows:

    public interface ValueProducerFactory {

        <T> Supplier<T> createValueProducer(String producerName, List<Object> creationParameters) throws ValueProducerCreationException;

    }

I have a class named CachingValueProducerFactory that implements the interface

    @Override
    public <T> Supplier<T> createValueProducer(String producerName, List<Object> creationParameters) throws ValueProducerCreationException {
        Map<List<Object>, Supplier<?>> parametersToOperatorsMap = producersCache.computeIfAbsent(producerName, s -> new HashMap<>());

        List<Object> key = Optional.ofNullable(creationParameters).orElse(Collections.emptyList());

        if (!parametersToOperatorsMap.containsKey(key)) {
            parametersToOperatorsMap.put(key, nestedProducersFactory.createValueProducer(producerName, creationParameters));
        }

        return (Supplier<T>) parametersToOperatorsMap.get(key);
    }

It seems like using Collections.emptyList() in the test is the problem, but I don't see any other solution for this.

答案1

得分: 1

你正在尝试同时模拟两个方法。在这一行中：

Mockito.when(valueProducerFactory.createValueProducer("IdProducer", Collections.emptyList()).get()).thenReturn(mappedValue);

你正在调用createValueProducer()调用的结果上的get()方法，因为你还没有模拟它，所以它是null。

有两种解决方案：

使用深度存根：

ValueProducerFactory valueProducerFactory = Mockito.mock(ValueProducerFactory.class, Mockito.RETURNS_DEEP_STUBS);
Mockito.when(valueProducerFactory.createValueProducer("IdProducer", Collections.emptyList()).get()).thenReturn(mappedValue);

首先模拟Supplier（注意已删除的get()）：

Supplier<Object> supplier = () -> mappedValue;
ValueProducerFactory valueProducerFactory = Mockito.mock(ValueProducerFactory.class);
Mockito.when(valueProducerFactory.createValueProducer("IdProducer", Collections.emptyList())).thenReturn(supplier);

Mockito.when(valueProducerFactory.createValueProducer("IdProducer", Collections.emptyList()).get()).thenReturn(mappedValue);

ValueProducerFactory valueProducerFactory = Mockito.mock(ValueProducerFactory.class, Mockito.RETURNS_DEEP_STUBS);
Mockito.when(valueProducerFactory.createValueProducer("IdProducer", Collections.emptyList()).get()).thenReturn(mappedValue);

Supplier<Object> supplier = () -> mappedValue;
ValueProducerFactory valueProducerFactory = Mockito.mock(ValueProducerFactory.class);
Mockito.when(valueProducerFactory.createValueProducer("IdProducer", Collections.emptyList())).thenReturn(supplier);