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: predefined_spec.rb
    path of file: ./repos/natalie/spec/language
    
    the code of the file until where you have to start completion: require_relative '../spec_helper'
require 'stringio'

# The following tables are excerpted from Programming Ruby: The Pragmatic Programmer's Guide'
# Second Edition by Dave Thomas, Chad Fowler, and Andy Hunt, page 319-22.
#
# Entries marked [r/o] are read-only and an error will be raised of the pro
    
    def foo
      outer = StandardError.new 'outer'
      inner = StandardError.new 'inner'

      begin
        raise outer
      rescue
        $!.should == outer

        # nested rescue
        begin
          $!.should == outer
          raise inner
        rescue
          $!.should == inner
          return
        ensure
          $!.should == outer
        end