Testing

unit tests are more modular and work within specific packages. they assume everything else is working and only test a small functionality. they are a programmer's friend.

functional tests treat the entire system as a black-box; i.e. if the program manipulates data, the functional tests go check to see if the data has been manipulated correctly.

functional tests are more involved, and trickier to design. you may need to use profiling tools to find them, and the skill of creating them is often best left to a separate team that enjoys finding bugs.