rspec/rspec-support — pull request #8 by JonRowe (2013-12-01 07:13:55+00:00)
Title: core-less `warn_with` disregards `:replacement`

...but it should use it. For example:

https://github.com/rspec/rspec-mocks/blob/1cd11ee5e39b08f0e4e38afff736767186dce933/lib/rspec/mocks/warnings.rb#L30-L34