It's used across apps:
```
λ ack -l assert_compile_fail 
lib/elixir/test/elixir/kernel/errors_test.exs
lib/elixir/test/elixir/kernel_test.exs
lib/ex_unit/lib/ex_unit/assertions.ex
lib/ex_unit/test/ex_unit/doc_test_test.exs
```

Should I construct relative paths from `lib/ex_unit/test` into `lib/elixir/test`?