tests: fix broken tests

[ilyaZar]

Small fix for tests/testthat/test-with_opt.R but improves codecov for R/with_opt.R from 9.68% to 100% and overall package covr a bit.

Fix #1119

[ColinFay]

Note to self : have to look into this bcs I think running load_all() inside the tests themselves might have some weird side effects 🤔 Do we do this already?

[ColinFay]

Hey,

Thanks for working on this.

I've worked on a full refactoring of the test suite, so this won't be needed anymore :)

The two main goals of the test refactoring has been :

• remove noisy prints to the console
• don't manipulate the R session (no load_all() and set_here() and stuff like that), so it's more fast and reliable