My understanding of bundler is that when you add a Gem to the Gemfile, bundler will automatically install all its dependencies when you run
spec.add_development_dependency "bundler", "~> 1.7"
spec.add_development_dependency "rake", "~> 10.0"
spec.add_development_dependency "eventmachine", "~> 1.0.4"
eventmachine (>= 1.0.0.beta.1)
> require 'my_gem'
RuntimeError: Missing EM-Synchrony dependency: gem install mysql2
em-synchrony does not depend on
mysql2. It is merely a supported client, one of several: https://github.com/igrigorik/em-synchrony#em-synchrony
Indeed, looking at em-synchrony's gemspec reveals only one dependency
It is, however, a development dependency of em-synchrony as listed in the development group in its Gemfile. These dependencies won't get installed for you.
You'll have to manually include