:DESC
A non-existent encoding is specified. Boxes falls back to the system encoding and logs a warning.

:ARGS
-n NON-EXISTENT
:INPUT
foo
:OUTPUT-FILTER
s/( falling back to) .*$/\1 [system encoding]/
:EXPECTED
boxes: Invalid character encoding: NON-EXISTENT - falling back to [system encoding]
/*******/
/* foo */
/*******/
:EOF