[FR] Fix broken tests in `test-with_opt.R`

[ilyaZar]

The tests in tests/test-with_opt.R are defunct as the run_app() function is not properly sourced in a dummy-golem.

One can add a call to devtools::load_all() inside the test so the dummy golem has run_app() in its workspace. The test should run in non-interactive mode then.

Can be fixed via #1120