improve rspec speed GC

#spec/support/deferred_garbage_collection.rb
class DeferredGarbageCollection

  DEFERRED_GC_THRESHOLD = (ENV['DEFER_GC'] || 15.0).to_f

  @@last_gc_run = Time.now

  def self.start
    GC.disable if DEFERRED_GC_THRESHOLD > 0
  end

  def self.reconsider
    if DEFERRED_GC_THRESHOLD > 0 && Time.now - @@last_gc_run >= DEFERRED_GC_THRESHOLD
      GC.enable
      GC.start
      GC.disable
      @@last_gc_run = Time.now
    end
  end
end

#update rspec
config.before(:all) do
  DeferredGarbageCollection.start
end

config.after(:all) do
  DeferredGarbageCollection.reconsider
end

run as below:
DEFER_GC=20 rake spec