Component metadata is one of the most effective methods to improve the testability of component-based software. We give a formal definition of component, and summarize meanings of component metadata. Based on these, an idea of Grouped-Metadata Object (GMO) is introduced, which is divided into two types, respectively named descriptive metadata and operative metadata. And a general framework of descriptive metadata and operative metadata is further given, which is consisted of several groups. Each group includes several attributes, and their meanings are described. Furthermore, we give a formal reference model of GMO using class diagram of UML. And change model in GMO is described. Here we introduce a concept of Method Dependency Graph(MDG) to implement mapping component changes to component interface changes. Then the changes are reflected in relevant attributes in GMO provided to component users in order to facilitate regression testing. Finally the case study based on previous model is done, and the corresponding results are given. All these show effectively that the models we presented are valid and helpful for component-based software testing.