title: How to best test Java code?
body: <p>I have been working on a comparatively large system on my own, and it's my first time working on a large system(dealing with 200+ channels of information simultaneously). I know how to use Junit to test every method, and how to test boundary conditions. But still, for system test, I need to test all the interfacing and probably so some stress test as well (maybe there are other things to do, but I don't know what they are). I am totally new to the world of testing, and please give me some suggestions or point me to some info on how a good code tester would do system testing.</p>
  
  <p>PS: 2 specific questions I have are:
  how to test private functions? 
  how to testing interfaces and avoid side effects?</p>