As we move from developing procedure-oriented to object-oriented programs, the complexity traditionally found in functions and procedures is moving to the connections among components. More faults occur as components are integrated to form higher level aggregates of behavior and state. Consequently, we need to place more effort on testing the connections among components. Although object-oriented technology provides abstruction mechanisms to build components to integrate, it also adds new compositional relations that can contain faults, which must be found during integration testing. This paper describes new techniques for analyzing and testing the polymorphic relationships that occur in object-oriented software. The application of these techniques can result in an increased ability to find faults and overall higher quality software.