Agile rspec with let()

Rspec 1.3 has the least-used, yet significant feature called let().

Here's how you set up Rspec 2, for those who have not caught on to let().

describe Friendship do

 before :all do

   @users = (1..5).collect { Factory(:user) }

 end



 after :all do

   @users.each { |user| user.destroy! }

 end



 it 'should do something' do

   @users.each do |user|

     user.should be_valid

   end



   # Something interesting with @users

 end

end

You should be able to replace everything you use @variables for with let(), like this:

describe Friendship do

 let(:users) { (1..5).collect { Factory(:user) } }



 before :all do

   users

 end



 after :all do

   users.each { |user| user.destroy! }

 end



 it 'should do something' do

   @users.each do |user|

     user.should be_valid

   end



   # Something interesting with @users

 end

end

I prefer not to preload everything. The tradeoff is slower specs:

describe Friendship do

 let(:users) { (1..5).collect { Factory(:user) } }



 it 'should do something' do

   users.each do |user|

     user.should be_valid

   end

   # Something interesting with @users

 end

end

let() cleans up a lot of your code. But where it really shines comes in combination with two things: (1) rspec 2 will preload everthing under spec/support, and (2) Rails 3's secret weapon, ActiveSupport::Concern. You can factor out your let() declarations and share it across your spec, like so:

# Put this in spec/support/application.rb

module SpecHelpers

 module Application

   extend ActiveSupport::Concern



   included do

     let(:users) { (1..5).collect { Factory(:user) } }

   end

 end

end



# spec/friendship_spec.rb

# Rspec 2 automatically loads everything in spec/support

require 'spec_helper'



describe Friendship do

 include SpecHelpers::Application



 it 'should do something' do

   users.each do |user|

     user.should be_valid

   end

   # Something interesting with @users

 end

end



# spec/comment_spec.rb

require 'spec_helper'



describe Comment do

 include SpecHelpers::Application



 it 'should do something' do

   users.each do |user|

     user.should be_valid

   end

   # Something interesting with @users

 end

end

Scoping and Closure in Ruby 1.8

The other day, I had to wrote code in this form:

class_eval do
 [:foo, :bar].each do |a|
   _cache = :"@#{a}_cache"
   define_method a do
    _cache
   end
 end
end

I had to ask myself: does this really do what I expect? I know the define_method closes over the _cache variable, but is it really isolated in each iteration? Am I really referencing a different _cache on each iteration? I tried this in the Rails console:

=> [:foo, :bar]
irb(main):009:0> foo
=> :@foo_cache
irb(main):010:0> bar
=> :@bar_cache

Should this have been surprising? I suppose not.