Unit Testing in R

Introduction

Priyanka Gagneja
Lead Analyst at OnPoint Insights

Big Fan of R community

Agenda

What is Testing ?

What is a Unit in R ?

Why we need Unit Testing ?

When should we Test ?

The three right answers are:

• ALWAYS!
• EARLY!
• OFTEN!

What should we Test ?

Typical Coding Workflow

• Write a function.
• Experiment with it in the console to see if it works.
• Rinse and repeat.

Demo - Typical Coding Workflow

# Write a function
rescale <- function(x, r.out) {
  p <- (x - min(x)) / (max(x) - min(x))
  r.out[[1]] + p * (r.out[[2]] - r.out[[1]])
}

Demo - Typical Coding Workflow

# Write a function
rescale <- function(x, r.out) {
  p <- (x - min(x)) / (max(x) - min(x))
  r.out[[1]] + p * (r.out[[2]] - r.out[[1]])
}

# Experiment 
x <- rnorm(20)
r.out <- c(0.1, 1.4)
range(rescale(x, r.out)) == r.out

[1] TRUE TRUE

How to do Unit Testing ?

Demo - testthat

library(testthat)

# Write a function
rescale <- function(x, r.out) {
  p <- (x - min(x)) / (max(x) - min(x))
  r.out[[1]] + p * (r.out[[2]] - r.out[[1]])
}

# Experiment 

# x <- rnorm(20)
# r.out <- c(0.1, 1.4)
# range(rescale(x, r.out)) == r.out

Demo - testthat

library(testthat)

# Write a function
rescale <- function(x, r.out) {
  p <- (x - min(x)) / (max(x) - min(x))
  r.out[[1]] + p * (r.out[[2]] - r.out[[1]])
}

# Experiment 

# x <- rnorm(20)
# r.out <- c(0.1, 1.4)
# range(rescale(x, r.out)) == r.out

# Write a formal unit test
testthat::expect_that(range(rescale(x, r.out)), equals(r.out))

# testthat::expect_equal(range(rescale(x, r.out)), r.out)

How to automate Testing ?

• The easiest way to get started is with usethis.

• Assuming you’re in project directory, run usethis::use_test("function-name") , e.g usethis::use_test("rescale") to create a test file, and set up all the other infrastructure you need.

• Run tests in a single file - test_file(path = "./tests/testthat/test-rescale.R")

• If you’re using RStudio, press Cmd/Ctrl + Shift + T (or run devtools::test() if not) to run all the tests in a package.

Why testing is important?

• Seems like extra work but will save you time * Decreased frustration. Bugs appear very close to hard deadlines. Testing allows to quickly identify where the problem is and fix it.

• More confidence in the code * Better code structure. Code that is easy to test is usually better designed. Tests sometimes make you see large complicated functions and break them down into smaller, more manageable chunks.

• Make changes or updates without worrying too much * Make changes confidently because you know your tests will catch any issues.

References/Acknowledgements

Thank You