RSpec hierarchical data structure evolution

my_data.r

=begin
  Allows for a data structure to be safely evolved hierarchically during testing

  Example:

    context "with one try" do
      with_data tries: 1
      describe "with suppressed exceptions" do
        with_data raise_on_fail: false
        specify { retry_raise_hell(1, my_data).should be_nil }
        specify { retry_raise_hell(1, my_data.merge(return_on_fail: "failure")).should == "failure" }
      end
    end

  Data structures are maintained on a stack in thread-local storage for maximum safety.

  Multiple data structures can be maintained in parallel by passing a name argument.

  Hashes are automatically merged.

=end
module MyData


  module Helper
    KEY = :spx_rspec_my_data

    # Retrieves the stack for a data structure from thread-local storage
    def get_my_data_stack(name)
      Thread::current[KEY] ||= {}
      Thread::current[KEY][name] ||= []
      Thread::current[KEY][name]
    end
  end


  module ExampleGroupMethods
    include Helper

    # Use with_data to modify the data structure in example groups
    def with_data(data = {}, name = :my_rspec_data)
      my_data = get_my_data_stack(name)
      around do |example|
        begin
          if my_data.empty?
            new_top = data
          else
            top = my_data.last
            new_top = (top.instance_of?(Hash) && data.instance_of?(Hash)) ? top.merge(data) : data
          end
          #puts "\n#{my_data.length}: pushing #{new_top.inspect}"
          my_data << new_top
          example.run
        ensure
          #puts "\n#{my_data.length}: top is #{my_data.last}; popping"
          my_data.pop
        end
      end
    end
  end


  module ExampleMethods
    include Helper

    # Use my_data to refer to the current (top of the stack) data structure in examples
    def my_data(name = :my_rspec_data)
      get_my_data_stack(name).last
    end
  end


  def self.included(receiver)
    receiver.extend         ExampleGroupMethods
    receiver.send :include, ExampleMethods
  end

end