# File lib/serverspec/type/package.rb, line 4
      def installed?(provider, version)
        if provider.nil?
          backend.check_installed(@name, version)
        else
          check_method = "check_installed_by_#{provider}".to_sym

          unless backend.respond_to?(check_method) || commands.respond_to?(check_method)
            raise ArgumentError.new("`be_installed` matcher doesn't support #{provider}")
          end

          backend.send(check_method, @name, version)
        end
      end