add unit tests for install_binary with yarn
add unit tests for install_binary with yarn

instacart/heroku-buildpack-ruby,pkgr/heroku-buildpack-ruby,makifund/heroku-buildpack-ruby,pilotcreative/heroku-buildpack-ruby,jonseaberg/heroku-buildpack-turbo-sprockets,Genius/heroku-buildpack-ruby,pilotcreative/heroku-buildpack-ruby,makifund/heroku-buildpack-ruby,jonseaberg/heroku-buildpack-turbo-sprockets,tpope/heroku-buildpack-ruby-tpope,Scalingo/ruby-buildpack,tpope/heroku-buildpack-ruby-tpope,Genius/heroku-buildpack-ruby,ericboehs/heroku-buildpack-ruby,ruby/heroku-buildpack-www-ruby-lang,instacart/heroku-buildpack-ruby,mattmanning/heroku-buildpack-ruby-jekyll,pkgr/heroku-buildpack-ruby,mattmanning/heroku-buildpack-ruby-jekyll,andycroll/heroku-buildpack-jekyll,zunda/heroku-buildpack-ruby,donnykurnia/heroku-buildpack-ruby,orenyk/heroku-buildpack-ruby,heroku/heroku-buildpack-ruby,ericboehs/heroku-buildpack-ruby,zunda/heroku-buildpack-ruby,brightbytes/heroku-buildpack-ruby-without-assets-precompile,donnykurnia/heroku-buildpack-ruby,andycroll/heroku-buildpack-jekyll,orenyk/heroku-buildpack-ruby,brightbytes/heroku-buildpack-ruby-without-assets-precompile,heroku/heroku-buildpack-ruby,Scalingo/ruby-buildpack