Thanks for your contribution. I would like you to do two changes for this PR to be merged.

1. The test suite already contains GCD programs (e.g. gcd.alan and gcd.dana) and these files come with specific input and result files. Rather than creating new such files, I suggest you modify your gcd.pcl program to read the input and write its output in the same way as the gcd.alan one and add symbolic links to the gcd.input and gcd.result files instead of having new ones.
2. There is no digits_sum program in the test suite, so these input and result files should be new, but it's clear from your program that the result file will not be just a number but will also contain some message string. This needs to be added to the digits_sum.result file. (Note that it should have the extension .result, not .output.)