ralphGetsTested

An R-Ladies Philly workshop on unit testing on Nov 11, 2021. An accompanying blog post and workshop recording are now available.

Abstract

In this workshop, Shannon Pileggi and Gordon Shotwell discuss how to get started with unit testing in R, which is formal automated testing of functions within packages. We demonstrate handy functions in usethis and devtools, strategies for writing tests, debugging techniques, and broad concepts in function writing that facilitate a smoother testing process.

This workshop picks up exactly where we left our little ralph (aka R-Ladies Philly) package one year ago with “Your first R package in 1 hour: Tools that make R package development easy”. Participants will get the most out of this workshop if they review those materials in advance, or if they are already familiar with building R packages with devtools and usethis.

Packages

Please install, or update, the following packages in advance of the workshop:

• usethis, devtools, testthat, covr, and DT

• broom, glue

• dplyr, purrr, magrittr, and rlang (or tidyverse)

Get started

You can work either (1) locally or (2) with GitHub.

1. To work locally, click the green Code button and download the zipped ralphGetsTested repository.

2. To work through GitHub, fork and clone this repository with usethis::create_from_github("shannonpileggi/ralphGetsTested").

Keyboard shortcuts

• Ctrl + S for save file

• Ctrl + Shift + L for devtools::load_all()

• Ctrl + Shift + F10 to restart R

Resources

• R package developement cheat sheet

• Ch. 12 Testing in R packages by Hadley Wickham and Jenny Bryan

• Ch. 8.2 Signalling conditions in Advanced R by Hadley Wickham

• testthat documentation

• {usethis} user interface functions

• covr package

• Debugging

  • RStudio blog post by Jonathan McPherson Debugging with the RStudio IDE

  • Ch 22 Debugging in Advanced R by Hadley Wickham

• Indrajeet Patil's curated list of awesome tools to assist R package development.

Part 1: testing compute_corr()

Review the compute_corr() function and the available expectations in testthat.

• What can we test in compute_corr()?

• What should we test in compute_corr()?

• How much of the function code is covered by tests?

Part 2: challenge function

Add the awesome_rladies function to the package.

awesome_rladies <- function(v) {
  
  sapply(v, function(x) {
    if (x == 1) {
      verb <- "is"
      noun <- "RLady"
    }
    
    if (x > 1) {
      verb <- "are"
      noun <- "RLadies"
    }
    
    as.character(glue::glue("There {verb} {x} awesome {noun}!"))
  })
}

and execute the function with:

awesome_rladies(1)
awesome_rladies(2)
awesome_rladies(1:2)

• Can we break this up to make it easier to test?

• What type of object should the function output?

• What type of object does this function expect? Can we put up guardrails so the user doesn’t send the wrong thing? How do we test those guardrails?