Ruby: Rewrote StringIO tests
Ruby: Rewrote StringIO tests

Use shoulda and don't test features built-in to Ruby.

kickback/steam-condenser-ruby,jpalumickas/steam-condenser-ruby,bfosberry/steam-condenser-ruby,Arie/steam-condenser-ruby,koraktor/steam-condenser-ruby,hcool/steam-condenser-ruby