From: J2M <james2mccarthy@...>
Date: 2006-10-22T22:55:53+09:00
Subject: Re: How to test if a module/gem is installed

you can find all the installed gems with a version of this;

def find_my_gem(name)
  spec_dir = File.join(Gem.dir, "specifications")
  gems = Gem::SourceIndex.from_installed_gems(spec_dir)
  gems.each {|path, gem| return true if name == gem.name}
  return false
end

this is a bit of a hack together, but gives you the basic idea.