finalizer.rb

require 'minitest/autorun'

class X < Minitest::Test
  def make_lambda b
    ->(z) { b[:finalize] = true }
  end

  def test_finalizer
    hash = {}
    make_finalizer = ->() {
      x = Object.new
      ObjectSpace.define_finalizer(x, make_lambda(hash))
      nil
    }
    make_finalizer.()
    GC.start # Finalized objects get deferred until 2nd full GC
    GC.start
    assert hash[:finalize]
  end
end