rspec/rspec-expectations — pull request #330 by JonRowe (2013-10-03 02:02:24+00:00)
Title: Handle undefined encoding conversions

This is a fallback when matching encoding internally to just remove problem characters.
In practise I believe this is triggered by diffing ascii input with UTF-8 input.

One example is rspec/rspec-core#1093, I believe this is trying to diff UTF-8 korean characters
with us-ascii.