Please check the following RSpec issue

rspec/rspec-core#2767

Usage

# Clone the repo
# Navigate to it
$ bundle install

Reproduce the leak

$ bundle exec ruby test.rb

On the 10.000th iteration the process' memory is at ~800Mb.

Confirm fix

$ WITH_FIX=true bundle exec ruby test.rb

The process' memory has reached a plateau - on the 10.000th iteration it is at ~33Mb.