Other interesting things
one of the {tinytest} vignettes has “a few tips on packages and unit testing”
two nice visualisations of the TDD cycle, and of TDD-until-the-feature’s ready are in “Test-Driven Development with Python” by Harry Percival.
“R Packages” has a chapter about “testthat”
The RStudio “shiny” website has three articles / webinars on testing in shiny
chapter-section on testing in “Engineering Production-Grade Shiny Apps”