Why testing take so much time? (Mikalai Alimenkou, Ukraine)

Most of you work by iterative development approaches and regression testing is done in each iteration (at least I hope so). And quite frequently we see following picture: in one iteration testing is finished in time, but in the next one it is only 50% completed. WTF? We added small increment of functionality in this iteration! From such incidents managers (if you still have them) start to “analyze and tune” performance of testers. They usually use stats and metrics… May be some testers are fired during this