Modal testing strategies for OO software

The essential challenge in testing object-oriented software is to craft a practical test suite that exercises enough combinations of message sequence and state interactions to provide sufficient confidence. These interactions are often subtle and complex and therefore error-prone. If all classes were alike, it might be enough to devise tests based either on message sequence or state. Sometimes this suffices, but usually both views are needed. The notion of class modality characterizes class behavior differences to indicate an appropriate test strategy