We can't help you: We have no idea what a ZWebServiceClient is, or where you got it from.
You will need to go back to the source, and ask them: but the error message is very explicit:
processResponses.ZResponse = testClients.process("752ce6861badcaa88d7", processes);
process returns a string, not a
TestServices.processResponse.ZResponse
and there is no cast operator defined.