INVEST – An acronymn for getting the requirements right

While reading the ‘User stories applied’ by Mike Cohn, I came across this acronymn INVEST, which stands for;

I- Independent, this is all about avoiding dependencies between user stories

N- Negotiable, indicates that stories are negotiable. They are not written contracts or requirements that the software must implement

V- Valuable to purchasers or users

E- Estimatable, developers should be able to estimate user stories  

S – Small, enough to estimate

T – Testable, stories must be written so as to be testable

This acronym is suggested by Bill Wake, author of extreme programming explored and Refactoring work book.