# Inside config/environments/development.rb

# Do the following after every request to the server in development mode
ActionDispatch::Callbacks.to_cleanup do

  # If the gem's top level module is currently loaded, unload it
  if Object.const_defined?(:MyCoolGem)
    Object.send(:remove_const, :MyCoolGem)
  end

  # Instruct ruby to "unrequire" all of the gems files.
  # CAREFUL: make sure this only matches your gems files.
  $".delete_if {|s| s.include? "my_cool_gem"}

  # Re-require your gem 
  # Note: because we removed all files previously required they will be reloaded
  # even if you didn't use load/autoload in your gem.
  require "my_cool_gem"

end