The coverage criteria of verification techniques play an important role in software development and testing. The goal is to reduce the size of test suites to economize on time, and to ensure whether all statements (or conditions) are covered. We can use these criteria to track test progress, assess current situations, predict emerging events, and so on. Thus we can take the necessary actions upon early indications that testing activity is falling behind. Modified condition/decision coverage (MC/DC) was proposed by NASA in 1994, and had been widely adopted and discussed since then. As evident from the definition, MC/DC criterion is used to judge whether each Boolean operator can be satisfied or not. However, we find that the selected test cases sometimes may not be able to satisfy the original definition of MC/DC under some Boolean expressions. In this paper, we will propose a simple but useful method which focuses on all conditions of Boolean expression to practice MC/DC. Specifically, our proposed approach will use n-cube graph and Gray code to implement the MC/DC criterion. We will further show how to use the proposed method to differentiate the necessary and redundancy test cases. Finally, a practical regression testing tool, TASTE (Tool for Automatic Software regression TEsting), will be presented in this paper. An example is given to illustrate the detailed working process and is explained in detail.