用 Mockito 模拟一个 LinkedList 并注入它

Question

我正在尝试创建一个 LinkList 并尝试通过字段注入将其注入 class PlayDeck。 之后，我想从 CardDeck class 模拟一个方法。

@Mock
public LinkedList<CardDeck> decks = new LinkedList<>();

@InjectMocks
public PlayDeck mockDeck = new PlayDeck(6);

@Before
public void setup() {
 MockitoAnnotations.initMocks(this);
}
@Test
public void returnADiamond10OnDraw() {
 //given
 this.mockDeck = new PlayDeck(6);
 Card givenCard = Card.builder().color(CardColor.Diamond).face(CardFace.TEN).build();
 BDDMockito.given(this.decks.get(BDDMockito.anyInt()).draw())
     .willReturn(Card.builder().color(CardColor.Diamond).face(CardFace.TEN).build());
 //when
 Card card = this.mockDeck.drawCard();
 //then
 assertThat(card.getFace()).isEqualByComparingTo(givenCard.getFace());
 assertThat(card.getColor()).isEqualByComparingTo(givenCard.getColor());
}

还有我的 PlayDeck class

private LinkedList<CardDeck> decks = new LinkedList<>();

  /**
   * New Playdeck with the amount of decks you want in it
   *
   * @param amount - amount of decks you want to play with
   */
  public PlayDeck(final int amount) {
    for (int i = 0; i < amount; i++) {
      this.decks.add(new CardDeck());
    }
  }
  /**
   * Draws a Card
   *
   * @return Card that was drawn
   */
  public Card drawCard() {
    int randomInt = new Random().nextInt(this.decks.size());
    return this.decks.get(randomInt).draw();
  }

和 CardDeck class

List<Card> deck;

public Card draw() {
    final int randomInt = new Random().nextInt(51);
    return this.deck.remove(randomInt);
  }

这里的问题是每次运行测试时都会收到 NullPointerException。 我认为这是因为我的 LinkedList 卡组是 null。 但它应该通过 PlayDeck 构造函数填充。

有谁知道如何解决这一问题？ 谢谢！

编辑：堆栈跟踪：

java.lang.NullPointerException
    at com.buzzet.test.PlayDeckShould.returnADiamond10OnDraw(PlayDeckShould.java:68)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:567)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

Answer 1

试试下面的代码，我重构了一些行。

import static org.assertj.core.api.Assertions.assertThat;
import static org.mockito.ArgumentMatchers.anyInt;
import static org.mockito.Mockito.when;

public class PlayDeckShould {
    @Mock
    public LinkedList<CardDeck> decks = new LinkedList<>();
    
    @Mock
    public CardDeck cardDeck;
    
    @InjectMocks
    public PlayDeck mockDeck = new PlayDeck(6);
    
    @Before
    public void setup() {
        MockitoAnnotations.initMocks(this);
    }
    
    
    @Test
    public void returnADiamond10OnDraw() {
        //givens
        decks=this.mockDeck.decks;
        Card givenCard = Card.builder().color(CardColor.Diamond).face(CardFace.TEN).build();
        when(cardDeck.draw()).thenReturn(Card.builder().color(CardColor.Diamond).face(CardFace.TEN).build());
        when(decks.get(anyInt())).thenReturn(cardDeck);
        when(decks.size()).thenReturn(6);
        when(cardDeck.draw()).thenReturn(Card.builder().color(CardColor.Diamond).face(CardFace.TEN).build());
        Card card = this.mockDeck.drawCard();
        assertThat(card.getFace()).isEqualByComparingTo(givenCard.getFace());
        assertThat(card.getColor()).isEqualByComparingTo(givenCard.getColor());
    }

而不是 Mocking 甲板，你只需要调用mockDeck.getDecks() 。

您已经在 CardDack class 中填充了该卡片组，因此您需要调用该CardDack object相同属性的 getter 方法。