Tests are written with the Vim plugin testing framework, vim-themis.
How to execute tests:
$ cd path/to/github-complete.vim
$ git clone https://github.com/thinca/vim-themis
$ git clone https://github.com/Shougo/vimproc.vim.git # if not installed yet
$ ./vim-themis/bin/themis test/To use guard, execute guard at the root of repository.
$ cd path/to/github-complete.vim
$ guard --guardfile test/Guardfile