安装karma optional dep failed

学习Angular.js，也就很荣幸的用到了单元测试。

安装karma报错，optional dep failed

apart from the error you are getting (which is reported by npm / socket.io) you shouldn't be installing Karma globally. Only a CLI should be installed globally:

npm install -g karma-cli

See: http://karma-runner.github.io/0.12/intro/installation.html

问题解决。