Now, granted early 1.8's tests were sparse. RubySpec is a by-product of the alternative implementations and a couple of test attempts (http://blog.headius.com/2008/05/rubyspec-bringing-ruby-test-...).

A lot of developers continue to use MRI 1.8 despite 1.9.1 being out due to API changes. So you could still make the case that the main interpreter being used was at one point not well tested. However, forward progress in the language is tested, so there's nothing really to be remedied.