Unit Testing Local Functions (letfn) in Clojure?

manpreet Best Answer 2 years ago

I spent a couple of years doing Scheme "back in the day" and am now learning Clojure. One of the "best practices" in Scheme was to define helper functions within the parent function thus limiting their visibility from "outside." Of course back then TDD wasn't done (or known!) so testing such functions wasn't an issue.

I'm still tempted to structure Clojure functions this way; i.e., using letfn to bind helper functions within the main function. Of course testing such "local" functions is problematic. I realize I can define "private" functions, but this scopes the visibility to the namespace which helps, but is not as fine grained. If you come upon a letfn within another function it's pretty clear that the function is not available for general use.

So, my question is, can one test such local functions and if so, how? If not, then is there some convention to aid in code reading so that it's clear that a function has only one caller?

TIA, Bill