Abstract
I/O constraints are restrictions defined on the values of parameters of send or receive events in test sequences for test realization. I/O constraints generation is an important step when translating test sequences into abstract test suites. In this paper, a symbolic assignment substitution method is used to generate I/O constraints of test sequences derived from Extended Finite-State Machines (EFSM). The proposed method is simpler and combines the steps to determine feasibility of test sequence and to generate I/O constraints.