1. A computer program product for controlling instruction execution in a processing environment, the computer program product comprising: a storage medium readable by a processor and storing instructions for execution by the processor for performing a method comprising: executing one instruction routine of an instruction stream; employing, in response to executing the one instruction routine, single test to determine whether processing is to continue to another instruction routine of the instruction stream or fall through mainline processing to a test set; and executing the another instruction routine or the test set, in response to the determination, wherein the executing executes the test set and the test set selects a next test set to be performed in response to the processing again falling through mainline processing.