global

def runnable_contexts(contexts)
  if required_ruby_version
    contexts.select do |context|
      Gem::Version.new(context.executable.version) >= Gem::Version.new(required_ruby_version)
    end.tap do |result|
      if result.empty?
        raise "No Ruby executables conforming required_ruby_version (#{required_ruby_version}) are specified"
      end
    end
  else
    contexts
  end
end