Consider adding skips for tests relying on suggested packages

[michaelquinn32]

Hi!

I hope this finds you well.

Several tests rely on randomizr, a suggested package. For cases where this package might not be installed, it would be nice if these tests cases were skipped. Testthat has a tool for this: skip_if_not_installed().

Would you be interested in a PR?

Thanks!

[nfultz]

We would most def welcome a PR, although I am not sure if there are plans to cut a new release this school year. @acoppock ?