RSpec matcher for alias_method

alias_matcher.rb

# RSpec matcher for alias_method.
# https://gist.github.com/1950961
# Usage:
#
#     describe User do
#       it { should alias_from(:username).to(:email) }
#     end


RSpec::Matchers.define :alias_from do |alias_method|
  match do |subject|    
    begin
      subject.send(alias_method)
    rescue NoMethodError
      raise "expected alias_method from #{alias_method} to #{@original_method} but #{alias_method} is not defined"
    end
    
    subject.method(alias_method).should eq(subject.method(@original_method))
  end
  
  description do
    "RSpec matcher for alias_method"
  end

  failure_message_for_should do |text|
    "expected alias_method from #{alias_method} to #{@original_method}"
  end

  failure_message_for_should_not do |text|
    "do not expected alias_method from #{alias_method} to #{@original_method}"
  end
  
  chain(:to) { |original_method| @original_method = original_method }
end