A method and system for automated testing of a system such as a billing module in a telecommunication system is disclosed. In a first embodiment, test APIs, scenarios and configuration information are embedded into the module itself in a way such that, when testing is desired, tests may be conducted without any need for a dedicated test environment. Tests can be run from within the module itself, thereby eliminating the risk, expense and time required to use external testing systems and data to test the module. In another embodiment, operational data such as live operational orders are wrapped in test headers and are used as input data for testing purposes within the billing module. In this embodiment, test APIs may be embedded into all modules of an operational support system so that complete system end-to-end testing is possible without the use of dedicated external test equipment and processes.