Hi Suniti
As for CA App Test, We dont have any native support for testing on the mainframe, but we do have a Mainframe Bridge that works with agents on the mainframe however this is for the virtualization components.
If the mainframe has exposed services (MQ, webservice, or DB2) we are able to work with those components through our native steps in CA App Test. If you are trying to do something custom to talk to a propriety application, you can teach DevTest with a custom step on how to talk to the proprierity app (which may be something our services may be able to help)
If you are able to shell script what you need to do, you can always use the external command step in DevTest to make the call to your script to call into the mainframe.
Hopefully this will help
-Joe