How to run tests for the currently selected line

I'd like to be able to hit a shortcut like `cmd-shift-r` and have that automatically run, say, `mix test test/turtle/api/v3_test.exs:72`.

The message I'm getting is that run by line isn't supported by Elixir, but this command needs no knowledge of Elixir. It just needs to be able to run `mix test {FILE_ACTIVE}:{FILE_ACTIVE_LINE_NUMBER}`

What is the best way to accomplish this? Thanks!