如何为 static void 方法实现 doNothing()？

Question

Am trying to mock one static void method, I tried PowerMock but always getting NullPointer exception.

We are trying to mock the below call -

public Class XYZ{
  public void method1(){
     ....
     SampleClass.methodTypeStatic1().methodTypeStatic2("xyz", "mno", classVeriable);
}

And the main class is -

public class SampleClass implements SampleClassParent{

private static SampleClass var1;

public static SampleClass methodTypeStatic1(){
    if (var1 == null) {
        //Do something on var1
    }
    return var1;
}

public void methodTypeStatic2(String localVar1, String localVar2, DifferentStaticClass localVar3) {
    //Do something
}}

Am trying to mock the call like this way in my test class -

@RunWith(PowerMockRunner.class)
@PrepareForTest({SampleClass.class})
public class XYZTest{

   @InjectMocks
   XYZ xyzTestService;

   @Test
   public void testMethod1(){
     ...
     PowerMockito.mockStatic(SampleClass.class);
     PowerMockito.doNothing().when(SampleClass.methodTypeStatic1());
     xyzTestService.method1();
}

Also to be mentioned SampleClass.class is not a part of our code, we have imported this external class into our code base to perform some task.

Answer 1

If you want to mock a non-void method, you need to define the behaviour for this method on the mock. You get the doNothing for free (as this is what mocking does), however you need to define what the method is supposed to return.

Your test could look like this:

@Test
public void testMethod1() {

    SampleClass sample = new SampleClass();

    PowerMockito.mockStatic(SampleClass.class);
    PowerMockito.when(SampleClass.methodTypeStatic1()).thenReturn(sample);

    XYZ xyzTestService = new XYZ();
    xyzTestService.method1();
}

You didn't not mention any @Mock annotations, so using @InjectMocks does nothing for you besides creating the XYZ object.