How load files in a path different than lib (Elixir)

I trying to use a helper for a task in a testing. My folder structure is like this:

config/
lib/
test/
test/test_helper.exs
test/provider_test/(the test files are here)

And now what I want to do is this

config/
lib/
test/
test/test_helper.exs
test/provider_test/(the test files are here)
test/provider_test/helpers/(the helpers files... more or less, one for helper)

I tried to use this (inside a test):

HelperModuler.calling_function(args)

But I get this error:

 (UndefinedFunctionError) undefined function HelperModuler.calling_function/1 (module HelperModuler is not available)