promote_load_path

# File lib/rubygems.rb, line 835
  def self.promote_load_path(gem_name, over_name)
    gem = Gem.loaded_specs[gem_name]
    over = Gem.loaded_specs[over_name]

    raise ArgumentError, "gem #{gem_name} is not activated" if gem.nil?
    raise ArgumentError, "gem #{over_name} is not activated" if over.nil?

    last_gem_path = Gem::Path.path(gem.full_gem_path).add(gem.require_paths.last)

    over_paths = over.require_paths.map do |path|
      Gem::Path.path(over.full_gem_path).add(path).to_s
    end

    over_paths.each do |path|
      $LOAD_PATH.delete path
    end

    gem = $LOAD_PATH.index(last_gem_path) + 1

    $LOAD_PATH.insert(gem, *over_paths)
  end