Possible Duplicate:Why to let / not let developers test their own work Developers develop the code and software. Ya that means they know very well of what they have done. But why there is always a separate department in IT companies called as Testing department? (Mainly for testing developers outcome)Why a developer is not doing Testing his or her own code? Is it Testing department knows very well about developers code, if so how come?Thanks in advance. 
Why there is a testing team?
testing;development process