System level testing of multi-threading functionality including building independent instruction streams while honoring architecturally imposed common fields and constraints

A testing facility is provided to test the multithreading functionality of a computing environment. The testing of this functionality includes building independent instruction streams to test threads of a multi-threaded environment while honoring architecturally imposed common fields and constraints, if any, of the threads. Certain features may be enabled/disabled for all threads. The instruction streams generated for testing this functionality may vary from being identical for all the threads being tested to being totally different, such as having different architectures.