elixir-lang/elixir — pull request #2960 by bgianfo (2014-12-23 00:28:53+00:00)
Title: Add cover directory from 'mix test --cover' to default .gitignore

Notice this directory gets created in the root of the project when the --cover option is used with mix test.

These are generated files, dependent on the specific time you run the command, so it doesn't seem like most users would want to check them in.