I have written the following code to retrieve the list of Test Cases from QC, but the tsTestFactory is null, whereas when I evaluate its.tsTestFactory() it returns a Com4j object.
I was having a similar issue. Here is some code that worked for me to list the Test Instances in a Test Set (I was originally having trouble at line 34 using ITestFactory):
AppLog can be replaced with System.out.println(); in this example for debugging. I hope this helps!