The best CI platforms let you "Rebuild with SSH" or something similar, and instead of having the cycle of "change > commit > push > wait > see results" (when you're testing CI specific stuff, not iterating on Makefiles or whatever, assuming most of it is scripts you can run both locally and in CI), you get a URL to connect to while the job is running, so you can effectively ensure manually it works, then just copy-paste whatever you did to your local sources.