def make_hash
  h = {}
  5000.times { |i| h[:"key_#{i}"] = WeakRef.new("value_#{i}") }
  h
end

h = make_hash
puts "Checking reference is alive"
p h[:key_200].weakref_alive?

puts "Running GC"
GC.run(true)

puts "Checking reference is alive"
p h[:key_200].weakref_alive?