ruby-on-rails - コマンド 'rails server' を実行できません!

Question

テスト アプリケーションを作成し、バンドルとすべての gem をインストールしました。アプリにcdしてコマンド「rails s」または「rails server」を入力すると、次のように返されます。

/Library/Ruby/Gems/1.8/gems/bundler-1.1.1/lib/bundler/runtime.rb:213: warning: Insecure world writable dir /Library/Ruby/Gems/1.8 in PATH, mode 040777
gem install minitest
/Library/Ruby/Gems/1.8/gems/turn-0.9.6/lib/turn/minitest.rb:9:in `require': no such file to load -- minitest/unit (LoadError)
    from /Library/Ruby/Gems/1.8/gems/turn-0.9.6/lib/turn/minitest.rb:9
    from /Library/Ruby/Gems/1.8/gems/turn-0.9.6/lib/turn.rb:13:in `require'
    from /Library/Ruby/Gems/1.8/gems/turn-0.9.6/lib/turn.rb:13
    from /Library/Ruby/Gems/1.8/gems/bundler-1.1.1/lib/bundler/runtime.rb:68:in `require'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.1.1/lib/bundler/runtime.rb:68:in `require'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.1.1/lib/bundler/runtime.rb:66:in `each'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.1.1/lib/bundler/runtime.rb:66:in `require'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.1.1/lib/bundler/runtime.rb:55:in `each'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.1.1/lib/bundler/runtime.rb:55:in `require'
    from /Library/Ruby/Gems/1.8/gems/bundler-1.1.1/lib/bundler.rb:119:in `require'
    from /Applications/MAMP/htdocs/railsTestApp1/config/application.rb:7
    from /Library/Ruby/Gems/1.8/gems/railties-3.2.2/lib/rails/commands.rb:53:in `require'
    from /Library/Ruby/Gems/1.8/gems/railties-3.2.2/lib/rails/commands.rb:53
    from /Library/Ruby/Gems/1.8/gems/railties-3.2.2/lib/rails/commands.rb:50:in `tap'
    from /Library/Ruby/Gems/1.8/gems/railties-3.2.2/lib/rails/commands.rb:50
    from script/rails:6:in `require'
    from script/rails:6

何が欠けているのかを理解しようとしました。必死になって、gem minitest を /Ruby/Gems/ と /Ruby/Gems/1.8/gems/ にインストールしようとしましたが、ここで何をしているのかわかりません。だからお願いします、私は何を間違っていますか??