Railscasts - RSpec Matchers & Macros

#157

Apr 13, 2009

RSpec Matchers & Macros

You can improve the readability and remove duplication in RSpec by adding matchers and macros. Learn how in this episode.

Tags: testing tools

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Note: Unfortunately there are a couple problems with this episode. Special thanks to David Chelimsky for pointing them out.

Since RSpec 1.2.0, the method names for failure messages are failure_message_for_should and failure_message_for_should_not. The old method names are still supported, but will be deprecating
eventually. The code below has been updated to reflect the new method names.
Newer versions of RSpec offers a 3rd method for creating a custom matcher. We can apply it to this example and it would have proper error messages. Please see the documentation for details on how this works.

# spec_helper.rb
require File.dirname(__FILE__) + "/custom_matchers"
require File.dirname(__FILE__) + "/controller_macros"
# ...
config.include(CustomMatchers)
config.include(ControllerMacros, :type => :controller)

# spec/custom_matcher.rb
module CustomMatchers
  class OneMoreThan
    def initialize(expected)
      @expected = expected
    end

    def matches?(actual)
      @actual = actual
      @actual == @expected+1
    end

    def failure_message_for_should
      "expected #{@actual.inspect} to be one more than #{@expected.inspect}"
    end

    def failure_message_for_should_not
      "expected #{@actual.inspect} not to be one more than #{@expected.inspect}"
    end
  end

  def be_one_more_than(expected)
    OneMoreThan.new(expected)
  end
end

# spec/controller_macros.rb
module ControllerMacros
  def self.included(base)
    base.extend(ClassMethods)
  end
  
  module ClassMethods
    def it_should_require_admin_for_actions(*actions)
      actions.each do |action|
        it "#{action} action should require admin" do
          get action, :id => 1
          response.should redirect_to(login_url)
          flash[:error].should == "Unauthorized Access"
        end
      end
    end
  end
  
  def login_as_admin
    user = User.new(:username => "admin", :email => "admin@example.com", :password => "secret")
    user.admin = true
    user.save!
    session[:user_id] = user.id
  end
end

# article_spec.rb
article2.position.should be_one_more_than(article1.position)

# articles_controller_spec.rb
it_should_require_admin_for_actions :new, :create, :edit, :update, :destroy

# simple matcher
def be_one_more_than(number)
  simple_matcher("one more than #{number}") { |actual| actual == number+1 }
end

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25 comments

1. mike Apr 13, 2009 at 02:37

Do you do any testing with shoulda? after banging my head over rspec for the past few days i decided to give it a try but there is not much instruction out there. I bet this cast would have gotten me stick with rspec for a few more days if id seen it earlier. :-p

RSpec Matchers & Macros

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