shared_subject.rb

# spec/support/shared_subject.rb

module RSpecSharedSubjectMacros

  # Usage:
  # 1. Replace 'subject' with 'shared_subject' to share the first result acroos the whole context
  # 2. (optional) replace 'before(:each)' blocks with 'shared_setup'
  # 3. Done. The subject will be shared within one, single context (nested will be re-setup again)
  #
  # DANGER NOTE: Make sure you accept the disadvantages of this, such as:
  # - there's a class variable that stores the shared data
  #
  # - that variable is set only once, when the first spec is run within the context
  #
  # - that variable is set withing normal spec run (so all the setup/teardown should work fine)
  #
  # - all the future tests will only share the subject, any 'let'-s or others will still be re-setup
  #
  # - some assertions cannot be used on shared subjects (such as 'should render_template')
  #   because the actual action has not been executed and only the result has been provided
  #
  # - set-up in the spec against subject is basically ignored (subject isn't render in the following tests):
  #     it 'should be have NRAS' do
  #       proeprty.nras = true # does not matter. This should be in 'before' block
  #       should have_content 'NRAS Dwelling'
  #     end
  #
  # - database assertions (unless subject will return snapshot of data in custom format)
  #   are not possible because the database is normally reset between the specs
  #
  #
  # If there are leak-issues then the suite can be converted back to normal by:
  # 1. Replace shared_subject with subject
  # 2. Replace shared_setup with before blocks
  def shared_subject(*args, &block)
    class_attribute :shared_subject_cache

    # Reset the subject for the whole context
    #
    # ALL run in the context of an ExampleGroup instance
    before(:all)  { self.class.shared_subject_cache = { } }
    after(:all)   { self.class.shared_subject_cache = nil }

    subject(*args) { RSpecSharedSubjectMacros.evaluate_shared_subject(self, &block) }

    # Executed if the shared subject hasn't been cached yet (hopefully only once)
    def shared_setup(&block)
      before(:each) do
        if !self.class.shared_subject_cache[self.class]
          # puts "*** Setup on #{self.class.inspect} ***"
          instance_eval(&block)
        end
      end
    end
  end

  private

  def self.evaluate_shared_subject(me, &block)
    me.class.shared_subject_cache[me.class] ||= eval_within_example(me, &block)
  end

  def self.eval_within_example(me, &block)
    # puts "*** <-- subject eval --> ***"
    me.instance_eval(&block)
  end
end

RSpec.configure do |config|
  config.extend(RSpecSharedSubjectMacros)
end