Because of concurrency and non determinism, the inner states of a running distributed program should be considered a part from the start and the end states, when the program is to be tested and the validated. According to specification based testing, these inner states will tranform into event sequences through the ports of the program, and the co relations among these events, i.e. the set of event sequencing constraints should be provided by the program's specification. In this paper, the authors introduce the E CSPE (extended constraints on succeeding and preceding events), a method to formalize these event constraints. The E CSPE includes three basic discription rules, which correspond to three different types of such event constraints. Based on the consistency with and coverage of these event constraints by the event sequences produced by the program execution, the validity of the distributed implementation can be tested.