How to use Unit Testing v2.1.4

[eluser]a_h_abid[/eluser]
Apparently I see that there is a Unit Testing Library in v2.1.4. It is in user guide as well.
http://ellislab.com/codeigniter /user-gu...sting.html

So how do i use it? Where we put the test codes, In our main Controller or In a separate test file? If separate, how we use them?