当前正在使用Mockito从我的一个类中测试一种方法.我的班级包含一个List,并且该方法接受同一班级的对象.问题是当我尝试从对象遍历List时.我得到一个指向列表的空指针.在下面,您将看到代码片段.

private Shipment shipment;
private Shipment shipment2;
@Mock
private Order mockOrder1;
@Mock
private Order mockOrder2;
@Mock
private Order mockOrder3;
@Mock
private ArrayList<Order> mockShipmentOrders;
@Mock
private ArrayList<Order> mockShipmentOrders2;

@Before
public void setUp(){
    MockitoAnnotations.initMocks(this);
    mockShipmentOrders.add(mockOrder1);
    mockShipmentOrders.add(mockOrder2);
    mockShipmentOrders2.add(mockOrder3);
    shipment = new Shipment(1, mockShipmentOrders);
    shipment2 = new Shipment(2, mockShipmentOrders2);
}

@Test
public void test_mergeShipments_increasesByOneWhenAShipmentOfOneAddedToAShipmentORderSizeOfTwo(){
    shipment.mergeShipments(shipment2);
    assertEquals(3, shipment.getShipmentOrders().size());
}

上面可以看到我的模拟测试,下面是我的Class和方法：

公共类货运{

private long shipmentID;
private List<Order> shipmentOrders;

public Shipment(long shipmentID, List<Order> shipmentOrders){
    this.shipmentID = shipmentID;
    this.shipmentOrders = shipmentOrders;
}

public List<Order> getShipmentOrders(){
    return shipmentOrders;
}

public void mergeShipments(Shipment shipment2){     
    List<Order> existingShipment = shipment2.getShipmentOrders();
    for (Order order : existingShipment){
        shipmentOrders.add(order);
    }
}

当我运行测试时,我得到了以下行的java.lang.NullPointerException：for(Order order：existingShipment){
在mergeShipemts();中

问题是;是否可以模拟列表,调用该列表,然后在该模拟列表上运行foreach？

解决方法:

为什么您的示例无法正常工作并引发NullPointerException有一些基本问题.

>对模拟列表上的add()的调用实际上没有任何作用.默认情况下,模拟中的所有void方法均为“ no-ops”
>使用for-each语法遍历列表,在后台调用Collection.iterator().这将返回null,因为您尚未将Mockito设置为返回其他任何内容.

相反,我不会模拟该列表,而是传递实际列表. Arrays.asList()便于测试.

@Before
public void setUp(){
    MockitoAnnotations.initMocks(this);
    shipment = new Shipment(1, Arrays.asList(mockOrder1, mockOrder2));
    shipment2 = new Shipment(2, Arrays.asList(mockOrder3));
}

如果确定要模拟列表,则必须模拟其行为,即使add()实际上存储一些东西,而.iterator()返回迭代器.如下所述,这可能非常痛苦.我仅包括此内容以说明原理.

@Mock
private List<String> mockedList;

@Before
public void init() {
    MockitoAnnotations.initMocks(this);

    List<String> realList = new ArrayList<>();
    doAnswer(new Answer<String>() {
        @Override
        public String answer(InvocationOnMock invocation) throws Throwable {
            realList.add(invocation.getArgumentAt(0, String.class));
            return null;
        }

    }).when(mockedList).add(any());

    when(mockedList.iterator()).thenAnswer(new Answer<Iterator<String>>() {

        @Override
        public Iterator<String> answer(InvocationOnMock invocation) throws Throwable {
            return realList.iterator();
        }
    });

    mockedList.add("bar");
    mockedList.add("baz");
}

@Test
public void iterateOverMockedList() {
    for (String each : mockedList) {
        System.out.println(each);
    }
}