Unit Test for a service using JobManger api

Hi Everybody. 

I opened a previous ticket : https://experienceleaguecommunities.adobe.com/t5/adobe-experience-manager/mocking-jobmanager-in-junit-unit-test/td-p/429046 because i had issue on mocking annotations. 

I am opening a new ticket ( related to the previous ) because i will appreciate help or explanations that let me understand the process.

I have a service : scheduleJob. 

In that service i have a function scheduling a job. It will looks like :

class ScheduleJob...
public void startMyJob(String topic, Map<String, Object> jobProperties) {

    JobBuilder jobBuilder =jobManager.createJob(topic);
    jobBuilder.properties(jobProperties); Line XXX
    JobBuilder.ScheduleBuilder scheduleBuilder =jobBuilder.schedule(); 
    scheduleBuilder.cron(schedulerExpression);
    List<String> errors = new ArrayList<>();
    ScheduledJobInfo scheduledJobInfo=scheduleBuilder.add(errors);
    if(scheduledJobInfo==null){
           do Something
                }
    }
    else{
          do something else
    }

}

and in my unit test i have something like that : 

class scheduleJobTest {

    @Mock
    private JobManager jobManager;

    @Mock
    private JobBuilder jobBuilder;

    @Mock
    private JobBuilder.ScheduleBuilder scheduleBuilder;

    @InjectMocks
    private ScheduleJob scheduleJob = new ScheduleJob() ;


    AemContext aemContext = new AemContext();


    @BeforeEach
    void setUp() {
        aemContext.registerService(JobManager.class,jobManager);
        aemContext.registerService(JobBuilder.class,jobBuilder);
        aemContext.registerService(JobBuilder.ScheduleBuilder.class,scheduleBuilder);
        aemContext.registerInjectActivateService(ScheduleJob);
     }

@Test
startMyJob(){
  scheduleJob.startMyJob(); Line XXY
  assert...

}

And it gives me a null pointer exception at line XXY inside the function scheduleJob.startMyJob at Line XXX.

Maybe i am not understanding how it works and i am not using the right method to do it. But the idea is :

I mock the JobManager, JobBuilder and all the ref/services needed in my scheduleJob Class and then i can just call my function and test it in UnitTestClass. Or do i need to stub them ? If i do that, where is the point to call my function ?

If someone could help me it will be really nice

Thanks in advance,

Regards