Thru a series of refactorings of runstep(), I was able to write more testable internal subroutines and methods, and then write tests for them t/configure/143-auto_gmp-01.t thru 03.t. I also dealt with the skimply documentation by quoting from the GNU description of GMP.
Assuming no problems crop up in the next 24 hours, I will resolve the ticket. Thank you very much. kid51
