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: raise_error.rb
    path of file: ./repos/artichoke/artichoke-backend/vendor/ruby/spec/mspec/lib/mspec/matchers
    
    the code of the file until where you have to start completion: class RaiseErrorMatcher
  attr_writer :block

  def initialize(exception, messa
    
  def failure_message
    message = ["Expected #{format_expected_exception}"]

    if @actual
      message << "but got: #{format_exception(@actual)}"
    else
      message << "but no exception was raised (#{MSpec.format(@result)} was returned)"
    end