As times passes, new functions are added and old functions are modified or deleted in a software system. As a result, backward compatibility problem arises. The compatibility problem is even worse in software systems that depend on system files, because two different versions cannot co-exist in the same environment. Being a cloud service, the open-source cloud testing platform STF-CTP has this compatibility problem because STF-CTP needs to support multiple versions of the same testing tools. This thesis will analyze the structure of STF-CTP and propose a method to support multiple versions of the same testing tools. In the proposed method, service provider sets up environment of the tools and specifies which versions to provide. When user uploaded test script with a selected version specified, the platform will dispatch the test script to be executed in the environment that fits the version specification. In this way, the compatibility problem will be resolved.