add shinytest2 for testing run example and draft yaml for deploy

[cjrace]

Overview of changes

Prepared run_example() so we can deploy it on our shinyapps.io account.

Updated the run_example test to use shinytest2, which opens up the potential for more UI testing of components.

Fixed a bug in run_example() (found by the shinytest2 tests spitting out a warning) where we had two IDs with the same name:

While I was there I used styler on the R/run_example.R file, I think that accounts for most of the changes - just code formatting rather than substantive.

PR Checklist

• I have updated the documentation (if needed)
• I have added or updated tests for these changes (if applicable)
• I have tested these changes locally using devtools::check()

Reviewer instructions

Mostly just check the changes in run_example() app. If that's fine then I think this is good to in.

Once I've got the deployment working I'll update the docs to point to it, waiting until it's working to do that though.

I've prepared a draft yaml file for the deployment GitHub action, expecting I may need to do some trial and error on the master branch once this is merged to get it working, I've never deployed an app returned by a function in this way before (alternative could be to make an app folder within the inst/ directory and then make run_example() call shiny::runApp("inst/showcase_app") (or something to that effect. I'll try to make this way work first, and then if I need to make bigger changes to move code around I'll do it in a new PR.

[sarahmwong]

Thanks Cam! Teeny bugs spotted here - think these have just slipped through when we've been adding things over time - shiny tests will be a really neat way to avoid this in future 😄