I’d love to talk with someone who does mainframe testing.

What does mainframe testing entail?
How did you get into it?
What tools do you use?
How much do you work with COBOL, Z/OS, JCL, RPG, PL/I, etc?
How do you interface with the mainframe & software — terminals, virtualization, etc. ?
What challenges are unique to testing mainframe system and what is common?