Note: All APIs steem-ruby, steem-mechanize and radiator provide a file called steem.rb.
Note, as of radiator-0.4.7 (or just before, probably):

So there was a time when you could not require both radiator and steem-ruby in the same runtime. But now, they should co-exist fine.
RE: Using Steem-API with Ruby Part 17 — Bonus: Unit Testing