Why a tester is needed for testing?

Why a tester is needed for testing the application? Programmer can also do the black box testing very well, should we need testing team for testing

NOTE : [I][This question was asked by rameshkota][/I]

It is globally believed that a programmer (developer) can’t do black box testing for the following reasons. :confused:

Because developers follow a constructive approach to make the s/w application and testers have to work in destructive approach to break the s/w application (not literally :D ).

Because developers can’t contribute in different permutations and combinations of input to the system.

Because developers hunt for logic in development and programming more then possible bugs.

Because developers tend to be optimistic while developing s/w that right and correct input will be given to the s/w. :cool:

In any business, the use of personnel with specialized skills enhances an organization's ability to be successful in large, complex, or difficult tasks. It allows for both
a) deeper and stronger skills and
b) the contribution of differing perspectives.

For example, programmers typically have the perspective of 'what are the technical issues in making this functionality work?'. A test engineer typically has the perspective of 'what might go wrong with this functionality, and how can we ensure it meets expectations?'.

Technical people who can be highly effective in approaching tasks from both of those perspectives are rare, which is why, sooner or later, organizations bring in test specialists.

can a doctor cure his own son?

May be yes.

But when it comes for operation, there is something which we can't explain in words.

I think , my point is clear to all.

Developer will do the black box to prove that whatever he has made is working as required, but never prove that it will not do that, which it should not do.He will comment "it is our extra feature, and all".
That's why tester is required?

simply because the projects are too big, and we cannot expect developer to test! Programmer may create the program which in his view may be right, but the tester checks whether the program fits to the Client's requirement or not!

Testing requires creating test cases.Test cases should be selected intelligently!These test cases should check whether prog gives desired output or not!
i hop iam clear
:D

Its a very foolish kind of question .....

Study the SDLC and you could get the answer