It can sometimes be difficult to find the data if you do not know what to ask for. Typical keywords with mainframe testing include "batch testing", "3278 emulation", "MQ Series", "green screen", "CICS", "MVS", "DB2", "Cobol", and so on. Once you try a few you will find other links. You can also go to IBM's web sites (local or even international), and look for testing. IBM owns Rational testing tools, and they have a lot to say about host-based testing.