A method of testing a process that has undergone modification. The process consists of multiple steps, and execution of the process involves interaction with multiple interfacing systems. A step consists of, e.g., sending a transmission to an interfacing system. The process is executed in normal fashion by sending transmissions to interfacing systems and obtaining responses to the transmissions from the interfacing systems. The transmissions and the responses thereto obtained from the interfacing systems are stored in a simulator. After the process is modified by modifying a step of the process, the modified process is executed in such a manner that transmissions are sent to the simulator rather than to the interfacing systems. The simulator sends responses to the transmissions. It is determined whether the responses received from the simulator are the expected responses, based on the modification made to the process.