I'm hoping to follow a similar trajectory to you, but with Elixir instead of closure. At the moment though, I tend to do things the other way around: write the top level functions and then fill out the base functions.

So I'd start a module with

def whatever(something), do: something |> function1 |> function2 |> function3

Then I'll write function1, 2, and 3 and whatever helper functions they need. And so on until it works. Maybe doing it your way is a better approach: helps you think it through first.

(although I'm aware some would say that tests should come before everything else anyway)