Why there is need of testing?

This is a right question because, prior to the concept of TESTING software as a ‘Testing Project’, the testing process existed, but the developer(s) did that at the time of development. But you must know the fact that, if you make something, you hardly feel that there can be something wrong with what you have developed. It's a common trait of human nature, we feel that there is no problem in our designed system as we have developed it and it is perfectly functional and fully working. So the hidden bugs or errors or problems of the system remain hidden and they raise their head when the system goes into production. On the other hand, its a fact that, when one person starts checking something which is made by some other person, there are 99% chances that checker/observer will find some problem with the system (even if the problem is with some spelling that by mistake has been written in wrong way.). Really weird, isn't it? But that’s a truth! Even though its wrong in terms of human behavior, this thing has been used for the benefit of software projects (or you may say, any type of project). When you develop something, you give it to get checked (TEST) and to find out any problem, which never aroused while development of the system. Because, after all, if you could minimize the problems with the system you developed, it’s beneficial for yourself. Your client will be happy if your system works without any problem and will generate more revenues for you.