1. A system for testing software, the system generating a multi-level test case from a unified modeling language (UML) sequence diagram (SD), the multi-level test case being based on a multiple condition control flow graph (MCCFG), the system comprising: at least one processor and a memory unit; a unified modeling language (UML) sequence diagram (SD) metamodel storing unit which stores a unified modeling language (UML) sequence diagram (SD) metamodel therein; a multiple condition control flow graph (MCCFG) metamodel storing unit which stores a multiple condition control flow graph (MCCFG) metamodel; a model converting unit which converts the unified modeling language (UML) sequence diagram (SD) according to the unified modeling language (UML) sequence diagram (SD) metamodel and the multiple condition control flow graph (MCCFG) metamodel and generates the multiple condition control flow graph (MCCFG); and a coverage criteria unit which converts the multiple condition control flow graph (MCCFG) into a plurality of test cases.