Expecting 'hello world', but got ./test.rb:14:in `call_hello_world': undefined local variable or method `hello_world' for NameSpace::Bar:Module (NameError) from ./test.rb:19:in `<main>'

test.rb

#!/usr/bin/env ruby

module NameSpace
  module Foo
    def hello_world
      puts 'hello world'
    end
  end

  module Bar
    include Foo

    def self.call_hello_world
      hello_world
    end
  end
end

NameSpace::Bar.call_hello_world