java - 构造函数定义中的 NullPointerException

Question

我正在尝试测试以下类(class):

public final class ClassA {

  private final ClassB member;

  public ClassA() {
    this.member = new ClassB();
  }

}

下面是测试类:

@RunWith(PowerMockRunner.class)
@PrepareForTest({ClassA.class, ClassB.class})
public final class ClassATest {

  @Mock
  private ClassB mocked;

  private ClassA testClass;

  @Before
  public void initTest() {
    PowerMockito.whenNew(ClassB.class).withNoArguments().thenReturn(mocked);
    testClass = new ClassA();
  }

现在，问题是我得到一个 nullpointerexception，其堆栈跟踪如下所示:

java.lang.NullPointerException
  [junit]     at a.a.i.ClassA.<init>(ClassA.java:44)
  [junit]     at a.a.i.ClassATest.init(ClassATest.java:53)
  [junit]     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  [junit]     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
  [junit]     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  [junit]     at java.lang.reflect.Method.invoke(Method.java:606)
  [junit]     at org.junit.internal.runners.MethodRoadie.runBefores(MethodRoadie.java:132)
  [junit]     at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:95)
  [junit]     at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.executeTest(PowerMockJUnit44RunnerDelegateImpl.java:294)
  [junit]     at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTestInSuper(PowerMockJUnit47RunnerDelegateImpl.java:127)
  [junit]     at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTest(PowerMockJUnit47RunnerDelegateImpl.java:82)
  [junit]     at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runBeforesThenTestThenAfters(PowerMockJUnit44RunnerDelegateImpl.java:282)
  [junit]     at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:86)
  [junit]     at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:49)
  [junit]     at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.invokeTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:207)
  [junit]     at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.runMethods(PowerMockJUnit44RunnerDelegateImpl.java:146)
  [junit]     at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$1.run(PowerMockJUnit44RunnerDelegateImpl.java:120)
  [junit]     at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:33)
  [junit]     at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:45)
  [junit]     at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.run(PowerMockJUnit44RunnerDelegateImpl.java:122)
  [junit]     at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.run(JUnit4TestSuiteChunkerImpl.java:106)
  [junit]     at org.powermock.modules.junit4.common.internal.impl.AbstractCommonPowerMockRunner.run(AbstractCommonPowerMockRunner.java:53)
  [junit]     at org.powermock.modules.junit4.PowerMockRunner.run(PowerMockRunner.java:59)
  [junit]     at junit.framework.JUnit4TestAdapter.run(JUnit4TestAdapter.java:38)
  [junit]     at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.run(JUnitTestRunner.java:532)
  [junit]     at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.launch(JUnitTestRunner.java:1165)
  [junit]     at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.main(JUnitTestRunner.java:988)

ClassA 的第 44 行是 公共(public)类 A() {

ClassATest 的第 52 行是 testClass = new ClassA();

我以前从未在构造函数定义中遇到过 NullPointerException，所以我不知道该怎么做。任何帮助将不胜感激。

Answer 1

我知道这个问题是关于 NPE 的，但与其解决这个问题，不如重新考虑您的测试策略。为什么？

如果 ClassA 负责 ClassB 实例的创建和生命周期，而您决定不注入(inject) ClassB 的对象，为什么要尝试模拟它？你的测试不应该依赖于实现细节，所以如果你没有在任何地方注入(inject)它，你不应该模拟 ClassB。