Find Bundler gems in a given dependency group.

gemfile.rb

require 'bundler'

class Gemfile
  def initialize gemfile_path = 'Gemfile'
    @bundler = Bundler::Dsl.new
    @bundler.eval_gemfile gemfile_path
  end

  def gems group
    @bundler.dependencies.select do |gem|
      gem.groups.include? group
    end.map &:name
  end
end

gemfile = Gemfile.new
gemfile.gems :development
gemfile.gems :test