EXPRESSION ENGINE FOR TESTING TRANSACTION PROCESSING SYSTEM

A system receives a request to process data. The system uses an expression engine to apply one or more expressions to the data to perform one or more application programming interface (API) interactions, which may include one or more of: dynamic resolution of API endpoints, API payload construction, and validation of API payload data fields. The Expressions are predefined entities configured to perform actions involving the system. The system initiates the expression engine. The system executes an initial expression upon initial data to produce an expression result. Executing the initial expression can involve iteratively resolving an ordered set of related expressions.