Ruby 2.5+ doesn't support option -rubygems anymore. --- a/Rakefile +++ b/Rakefile @@ -18,7 +18,6 @@ require 'rake/testtask' Rake::TestTask.new 'test' do |t| t.test_files = FileList['test/test_*.rb'] - t.ruby_opts = ['-rubygems'] end # ==========================================================