Software development process contains various phases. More efforts and cost have to be spent in the testing phases. Test case generation at cluster level in Software Development Life Cycle (SDLC) can be the best optimized solution for reducing effort and cost. The efficient test cases will play a vital role in reducing the effort in Software Testing Life Cycle (STLC). Unified Modeling Language (UML) designs provide valid information for software development process. UML interaction diagram based test case generation can be used to improve the quality in software. This paper presents a method for test case generation from UML interaction diagram at the cluster level. It makes three major processes. First, interaction diagrams are converted to data structure stack, and then the stack stimulus are minimized using boundary testing, and finally the test case is generated from minimized stack. This paper has presented our technique with some real time examples of embedded system software.