foo.rb

module Foo
  [:debug, :info, :warn, :error, :fatal].each do |level|
    define_method level do |msg|
      p 'dummy 1'
    end
  end
  module_function :debug, :info, :warn, :error, :fatal

  private
    def message(content, log_level)
      'dummy2'
    end
end

foo_spec.rb

require 'spec_helper'
require 'foo'
include Foo

describe 'Foo' do
  it 'raise Exception' do
    expect { raise Exception.new }.to raise_exception (Exception)
  end
end