This can be difficult to determine. Many modern software applications are so complex,and run in such an interdependent environment, that complete testing can never be done. Common factors in deciding when to stop are:
What can be done if requirements are changing continuously?
What if the application has functionality that wasn�t in the requirements?
What should be done after a bug is found?
What is a test case?
What software tools are in demand these days?
Why are there so many software bugs?
What is software quality assurance?
What is an inspection?
What is the difference between verification and validation?