To efficiently decide input data of an API to be executed and indicate a candidate for an API to be executed, a tool for testing a scenario which sequentially executes a plurality of APIs includes an API test control unit that stores, with the execution of the API, sequence data indicating an execution sequence of the APIs and input and output data in a test information database via an API sequence registering unit. Association data indicating association of input and output data between the APIs is also stored in the test information database via an association registering unit. Responsively, the API test control unit displays a candidate API list indicating one or more candidates for an API to be executed next based on the sequence data, and decides the input data of the API to be executed next based on the association data.