A selective regression testing algorithm is said to be safe if it does not miss any error revealing test cases.
Precision measures the extent the algorithm omits the non-modification traversing test cases.
One of the important problems in regression testing is to efficiently select those test cases. Because the usefulness of selective regression testing largely depends on the speed of test case selection, an efficient algorithm is essential. Most of the previous works on the topic use graph theory or program dependence analysis to solve the problem. In this paper, we employ a formal language approach to understand the difficulties and present approximate solutions for the problem. We show that algorithms.