A fairly standard way around this is to make the package a Suggests: and to
condition the use in code (or tests) via
if (requireNamespace(pkageNameHere, quietly = TRUE) {
....
}
That method is described in Writing R Extensions too, and followed by a
(very) large nunber of packages.
Dirk
--
https://dirk.eddelbuettel.com | @eddelbuettel | edd@debian.org