Thanks @Eiji! This is a good example. I recommend you to start a discussion on Elixir issues tracker. We do not track comments or discussions on the forum as feature requests.
Note that it is unlikely that exporting ExUnit.Diff as is would be useful to you, as the current algorithm is recursive on itself, and you want to support more data types than the ones we do. There are different ways we could solve this, for example, by making the recursive function an argument on ExUnit.Diff, introducing a protocol, or by breaking ExUnit.Diff into smaller, reusable bits. So when opening the issue, please make sure that you provide a more complete proposal with examples on how you believe the ExUnit.Diff should be exported.
