Let's speed up RSpec, yo. This Singleton version totally based on @joevandyk and @triskweline's work

deferred_garbage_collection.rb

class DeferredGarbageCollection
  include Singleton

  # One can set a different time period for the garbage collection, but 15 seemed good.
  DEFERRED_GC_THRESHOLD = (ENV['DEFER_GC'] || 15.0).to_f

  def initialize
    @last_gc_run = Time.zone.now
  end

  def self.start
    instance.start
  end

  def start
    GC.disable if DEFERRED_GC_THRESHOLD > 0
  end

  def self.reconsider
    instance.reconsider
  end

  # Checks if last run time exceeds the value of the time threshold and enables Garbage
  # Collection for a short cleanup. After that Garbage Collection is deferred again.
  def reconsider
    return unless DEFERRED_GC_THRESHOLD > 0 && Time.zone.now - @last_gc_run >= DEFERRED_GC_THRESHOLD
    GC.enable
    GC.start
    GC.disable
    @last_gc_run = Time.zone.now
  end
end