A software testing system for generating a test job control language (JCL) file is provided. The system includes a processor, a memory device for storing a source JCL file containing jobs and an instruction file containing instructions for modifying the source JCL file according to a test environment. A JCL generation module executed by the processor determines all procedures that are referenced by the jobs in the source JCL file, opens each unique procedure of the determined procedures once and modifies the jobs in the source JCL file based on the instruction file and the opened procedures to generate the test JCL file. By opening each procedure only once which may be called multiple times in the jobs, the JCL generation module substantially increases the speed of generating the test JCL file.