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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.

merged by yannis Apr 4 '12 at 4:09

This question was merged with Why to let / not let developers test their own work because it is an exact duplicate of that question.