Question

我正在尝试测试以下类：

public final class ClassA {

  private final ClassB member;

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

}

以下是测试类：

@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，其堆栈跟踪看起来像：

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第44行是 public ClassA（）{

ClassATest的第52行是 testClass = new ClassA（）;

我从来没有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，但是你应该重新考虑你的测试策略，而不是解决这个问题。为什么呢？

如果ClassA负责ClassB实例的创建和生命，并且您决定不注入ClassB的对象，为什么要尝试模拟它？您的测试不应该依赖于实现细节，因此如果您没有在任何地方注入它，就不应该模拟ClassB。

Answer 2

这种做法根本不值得推荐。对象不应该负责创建自己的依赖项。它们应该在它们的构造函数中提供（或通过setter方法）。

我建议你改变你的构造函数

public final class ClassA {

  private final ClassB member;

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

}

如果你想保留你的代码，你可以添加一个在测试中使用的构造函数（尽管不建议仅为测试目的添加代码）

public final class ClassA {

  private final ClassB member;

  public ClassA() {
    this(new ClassB());
  }

  // Default visibility so it's only visible in its package
  // Added for testing purposes
  ClassA(ClassB member) {
    this.member = member;
  }

}

Answer 3

我想当你宣布成员为最终时你应立即实例化它在转到构造函数之前尝试这样做，看看会发生什么

构造函数定义中的NullPointerException

3 个答案: