Add tests for github client.
Add tests for github client.

christophelec/nbviewer,roxyboy/nbviewer,AlfiyaZi/nbviewer,Jay-Oh-eN/nbviewer,Jay-Oh-eN/nbviewer,christophelec/nbviewer,bollwyvl/nbviewer,bollwyvl/nbviewer,AlfiyaZi/nbviewer,thomasyu888/nbviewer,iamjakob/nbviewer,roxyboy/nbviewer,iamjakob/nbviewer,thomasyu888/nbviewer