I would be extremely hard to do because of two things:
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the very tenuous mapping between Elixir’s AST and the macro-expanded version. This makes it very hard to count which branches we covered, because the branches in the macro-expanded code are not necessarily related to the branches in the original code
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It’s very hard to get the Elixir AST for a given module. You’d have to use files as compilation units, and not modules.
Maybe it’s not as hard as I think it is, but it’s certainly not very easy. It’s much easir to get access to and manipulate the Erlang abstract format. I mean, I can’t even find a way to expand something inside a defmodule into Elixir AST. That’s probably because defmodule acts more like a function that creates a module and injects it into the running BEAM instance than a macro that is expanded into something more basic.
I guess this probably means there isn’t even a “fully expanded ast” for me to look at. But there must be something that the Elixir compiler feeds into the Erlang compiler, right?
