rspec/rspec-core — pull request #1190 by myronmarston (2013-11-18 07:13:01+00:00)
Title: Rubinius uses slightly different phrasing for this error.

Missing or uninitialized constant: RSpec::Core::SomeUndefinedConst

...rather than:

uninitialized constant RSpec::Core::SomeUndefinedConst