How do I mock a method with void return type in JMockit?

Question

I'm using TestNG and JMockit for testing. My code goes like this:

public boolean testMethod(String a, String b) {
   //processing .....
   mockClass.mockMethod(a);
   //processing....
}

The mockMethod():

Class MockClass {
     public void mockMethod(String a) {
        //some operations to mock
     }
 }

I'm using MockUp according to this question: (How to mock public void method using jmockit?)

I'm still getting the NPE. What am I doing wrong? Also, is it because I'm using it like this?

@Test
public void test() {
   new Expectations() {
       {
       //for statements preceding mockMethod()....
       new MockUp<MockClass>(){
           @Mock
           public void mockMethod(String a) {
               //do nothing
           }
       };
       }
   };
 }

I've put it outside Expectations() & used NonStrictExpectations too. How do I fix this?

Answer 1

If the method to be mocked is not returning anything, you don't need to do anything special in expectations. You can define your class to be mocked using @Injectable or @Mocked annotations in usual way. Optionally you can add an expectation to verify the number of times the method is called. Also you can add verification step to capture the argument "a" and do assertions on that. Refer below code sample.

@Tested
private MyClassToBeTested myClassToBeTested;
@Injectable
private MockClass mockClass;

@Test
public void test() {
    // Add required expectations
    new Expectations() {{
        ...
        ..
    }};

    // Invoke the method to be tested with test values;
    String expectedA = "testValueA";
    String expectedB = "testValueB";
    boolean result = myClassToBeTested.testMethod(expectedA, expectedB);

    // Assert the return value of the method
    Assert.assertTrue(result);

    // Do the verifications and assertions
    new Verifications() {{
        String actualA;
        mockClass.mockMethod(actualA = withCapture()); times = 1;
        Assert.assertNotNull("Should not be null", actualA);
        Assert.assertEquals(actualA, expectedA);
        ...
        ..
    }};

}