Assert null is not working as actual method changes the value - junit

Question

I am trying to write a Junit for a piece of code for asserting the value as null. But the value is changing on the actual call.
Main Class Code
#Activate
public void activate(ComponentContext context)
{
myNotificationSubscriber = NotificationSubscriber.newInstance(myGlobalTableNotificationService,
NotificationType.ENTITIES,
this);
setWantedSubscriptionStatus();
LOG.debug("Activating {} service", getClass().getName());
try
{
applyConfigUpdate(context, IS_ACTIVATION);
}
catch (ServiceNotAvailableException e)
{
String instanceNameWithException = COUNTER_INSTANCE_COBA.concat("-")
.concat(String.valueOf(e.getResponseCode().getResponseCode()))
.concat(e.getClass().getSimpleName());
myCounterregistrator.get()
.incrementCounter(Counter.DATAACCESS_COBA_RESPONSE_UNSUCCESSFUL.getCounterInstance(instanceNameWithException));
LOG.debug("Can not activate Component :{}", e.getMessage());
}
LOG.info("COBA Cache state is {}", myCacheState);
}
private GlobalTableRetriever getGlobalTableRetrieverer() throws ServiceNotAvailableException
{
GlobalTableRetriever tableFetcher = myGlobalTableRetriever.get();
if (tableFetcher == null)
{
throw new ServiceNotAvailableException(RETRIEVER_SERVICE_NOT_AVAILABLE_MSG, ResponseCode.COBA_READ_DATA_TEMPORARY_ERROR);
}
return tableFetcher;
}
I want to write the test for the catch block. So tried to write the test case in below.
#Test
public void testapplyConfigUpdate() throws GlobalTableException
{
exception.expect(ServiceNotAvailableException.class);
globalTableRetriever.set(null);
tableFetcher = globalTableRetriever.get();
assertThat(tableFetcher).isNull();
myTableHandler.activate(myOsgiComponentContext);
verify(myCounterRegistratorService, times(1)).incrementCounter(any(CounterInstance.class));
}
But once its entering to getGlobalTableRetrieverer method, the assertion null value is changing to original.

Answer 1

Why do you even need to assert that?
exception.expect(ServiceNotAvailableException.class);
already implies that tableFetcher is null.
Just try this :
#Test
public void testapplyConfigUpdate() throws GlobalTableException
{
exception.expect(ServiceNotAvailableException.class);
globalTableRetriever.set(null);
tableFetcher = globalTableRetriever.get();
}