Trying to handle Singleton in a more flexible way

gistfile1.rb

=begin
PRO:
* Configuration is easily testable (you can reset the singleton before each test)
* Configuration keeps Singleton behavior outside of its responabilities
=end

class Configuration
  def initialize(path: nil)
    puts "#initialize"
    @path = path
    # do some stuff, for example load the yaml located at @path
  end
  
  # define here the required helper methods
end
# ==> nil

module ConfigurableSingleton
  def self.included(base)
    base.class_eval do

      def self.setup(**options)
        @instance = reference_class.new(options) unless @instance
      end

      def self.instance
        @instance || raise('init with .setup first')
      end

      def self.reset
        @instance = nil
      end

      private_class_method :new

      def self.reference_class
        @reference_class || raise('provide a reference class with .use_class')  
      end

      def self.use_class(klass)
        @reference_class = klass
      end

    end
  end

end
# ==> nil

class ConfigurationProvider
  include ConfigurableSingleton
  use_class Configuration
end
# ==> Configuration

ConfigurationProvider.setup(path: 'foo')
# =#initialize
# ==> #<Configuration:0x007f91da102840 @path="foo">
ConfigurationProvider.instance
# ==> #<Configuration:0x007f91da102840 @path="foo">
ConfigurationProvider.reset
# ==> nil
ConfigurationProvider.setup(path: 'moo')
# =#initialize
# ==> #<Configuration:0x007f91da8b6be0 @path="moo">
ConfigurationProvider.instance
# ==> #<Configuration:0x007f91da8b6be0 @path="moo">
ConfigurationProvider.new
# =NoMethodError: private method `new' called for ConfigurationProvider:Class
# = from (irb):54
# = from /usr/bin/irb:12:in `<main>'