It is possible to do enough testing but determining the how much is enough is difficult. Simply doing what is planned is not sufficient since it leaves the question as to how much should be
Why is testing necessary?
Testing is necessary because the existence of faults in software is inevitable. Beyond fault-detection, the modern view of testing holds that fault-prevention (e.g. early fault detection/removal from requirements, designs etc. through static
In order to gain the most of the testing activities, a defined process must be followed. But before any testing activity begins, much of the effort should be spent on producing a good test plan