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: complain.rb
    path of file: ./repos/truffleruby/spec/mspec/lib/mspec/matchers
    
    the code of the file until where you have to start completion: require 'mspec/helpers/io'

class ComplainMatcher
  def initialize(complaint = nil, options = nil)
    # the proper solution is to use double spla
    
  def negative_failure_message
    if @complaint.nil?
      ["Unexpected warning: ", @warning.chomp.inspect]
    elsif @complaint.kind_of? Regexp
      ["Expected warning not to match: #{@complaint.inspect}", "but got: #{@warning.chomp.inspect}"]
    else
      ["Expected warning: #{@complaint.inspect}", "but got: #{@warning.chomp.inspect}"]
    end