PowerMock，模拟一个使用静态方法的类的方法 throw nullpointerexception答案

【问题标题】：PowerMock, mock a method of a class that uses a static method throw nullpointerexceptionPowerMock，模拟一个使用静态方法的类的方法 throw nullpointerexception
【发布时间】：2023-03-10 12:01:01
【问题描述】：

我想测试 ClassA 的方法，它的构造函数使用 ClassB 的静态方法。

类

public class ClassA
{
    private String something;
    private ClassC somethingElse;

    public ClassA(String parameter)
    {
        super(parameter);
        setClassC(ClassB.getClassC());
    }

    public ReturnClass methodToTest()
    {
        // do something...
    }
}

public class ClassB
{
    public static ClassC getClassC()
    {
        // do something and return ClassC
    }
}

测试类

@Test
@PrepareForTest(ClassB.class)
public void test_methodToTest() throws Exception 
{
    //Given
    parameter = Mockito.mock(String.class);
    aClassC = PowerMockito.mock(ClassC.class);
PowerMockito.mockStatic(ClassB.class);
    ClassA aClassA = new ClassA(parameter);

    //When
    PowerMockito.when(ClassB.getClassC()).thenReturn(aClassC);
    // Some behavior to test the method

    //Then
    ReturnClass aReturn = aClassA.methodToTest();
    assertNull(aReturn);
}

运行测试时，我得到一个 NullPointerException 如下：

异常

Java.lang.NullPointerException
    at ClassB.getClassC(ClassB.java:285)
    at ClassA.<init>(ClassA.java:72)
    at ClassATest.test_methodToTest(ClassATest.java:56)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    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:271)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.mockito.internal.runners.JUnit45AndHigherRunnerImpl.run(JUnit45AndHigherRunnerImpl.java:37)
    at org.mockito.runners.MockitoJUnitRunner.run(MockitoJUnitRunner.java:62)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)

我不知道如何模拟构造函数ClassA 和ClassB 的静态方法来测试ClassA 的方法。

【问题讨论】：

标签： java junit mocking mockito powermockito

【解决方案1】：

我想，你应该把PowerMockito.when放在lassA aClassA = new ClassA(parameter);之前

@Test
@PrepareForTest(ClassB.class)
public void test_methodToTest() throws Exception 
{
    //Given
    parameter = Mockito.mock(String.class);
    aClassC = PowerMockito.mock(ClassC.class);
    PowerMockito.mockStatic(ClassB.class);
    //When
    PowerMockito.when(ClassB.getClassC()).thenReturn(aClassC); 
    ClassA aClassA = new ClassA(parameter);
    // Some behavior to test the method

    //Then
    ReturnClass aReturn = aClassA.methodToTest();
    assertNull(aReturn);
}

【讨论】：