1. A computer-implemented method of generating test data for web services testing, comprising: loading a selected web service definition file describing one or more web services operations and associated schema file into memory; identifying an operation contained in said loaded file; identifying one or more fields used as one or more input parameters in said operation; receiving user customization of said one or more fields; validating automatically said user customization of said one or more fields against one or more original constraints specified in the selected file or the associated schema file or combinations thereof; configuring one or more generation rules, wherein the generation rules specify a test strategy for testing said one or more web services; and generating one or more variations of said one or more field based on the configured one or more generation rules.