: Object-oriented frameworks have extended reusability of software from code modules to architectural and domain information. This paper further extends software reusability from code and architecture to built-in tests (BITs) in object-oriented framework development. Methods for embedding BITs at object and object-oriented framework levels are addressed. Behaviours of objects and object-oriented frameworks with BITs in the normal and test modes are analyzed. Systematic reuse methods of BITs in object-oriented framework development are provided. The most interesting development in the paper is that the BITs in object-oriented frameworks can be inherited and reused as that of code. Therefore testability and maintainability of the test-built-in object-oriented frameworks can be improved by the BIT approach. The BIT method can be used in analysis, design and coding of object-oriented frameworks. Key words: Software engineering, object-oriented technology, framework, pattern, code reuse, fr...