Risk-based testing (RBT) is a type of http://www.answers.com/topic/software-testing - software testing that prioritizes the features and functions to be tested based on priority/importance and likelihood or impact or failure. In theory, since there is an infinite number of possible tests, any set of tests must be a subset of all possible tests. Test techniques such as boundary value analysis and state transition testing aim to find the areas most likely to be defective. So by using test techniques, a software test engineer is already selecting tests based on risk.