You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: combined_experiments_helper.rb
    path of file: ./repos/split/lib/split
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

module Split
  module CombinedExperimentsHelper
    def ab_combined_test(metric_descriptor, control = nil, *alternatives)
      return nil unless experiment = find_combined_experiment(metric_descriptor)
      raise(Split::InvalidExperimentsFormatError, "Unable to find experiment #{metric_descriptor} in configuration") if experiment[:combined_experiments].nil?

      alternative = nil
      weighted_alternatives = nil
      experiment[:combined_experiments].each do |combined_experiment|
        if alternative.nil?
          if control
            alternative = ab_test(combined_experiment, control, alternatives)
          else
            normalized_alternatives = Split::Configuration.new.normalize_alternatives(experiment[:alternatives])
            alternative = ab_test
    
    def ab_combined_test(metric_descriptor, control = nil, *alternatives)
      return nil unless experiment = find_combined_experiment(metric_descriptor)
      raise(Split::InvalidExperimentsFormatError, "Unable to find experiment #{metric_descriptor} in configuration") if experiment[:combined_experiments].nil?

      alternative = nil
      weighted_alternatives = nil
      experiment[:combined_experiments].each do |combined_experiment|
        if alternative.nil?
          if control
            alternative = ab_test(combined_experiment, control, alternatives)
          else
            normalized_alternatives = Split::Configuration.new.normalize_alternatives(experiment[:alternatives])
            alternative = ab_test(combined_experiment, normalized_alternatives[0], *normalized_alternatives[1])
          end
        else
          weighted_alternatives ||= experiment[:alternatives].each_with_object({}) do |alt, memo|
            alt = Alternative.new(alt, experiment[:name]).name
            memo[alt] = (alt == alternative ? 1 : 0)
          end

          ab_test(combined_experiment, [weighted_alternatives])
        end