rspec/rspec-core — pull request #1206 by alexpeattie (2013-12-02 19:31:57+00:00)
Title: Don't allow the same formatter to be sent to the same output

Fix (or partial fix) for #1144.

This patch doesn't address the other potential issue - the case of multiple config files. Right now formatters specified in different configuration files override each other (rather than appending the additonal formatters, as is the case elsewhere).