Mainframe Testing is similar to client-server applications testing, but one needs to know how to operate basic TSO and ISPF commands and menus, view mainframe files, look at and use SDSF or other output tool, log on CICS and transactions, use FTP or another transfer protocol, submit the batch job - it's for QA testing of mainframe applications. And plus, unlike the QA testing for another platform, like WEB and/or client-service, the mainframe is usually back-end, it requires the needs and understanding of COBOL, DB2, JCL, CICS, Assembler, VSAM, ISPF/TPF.