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testing_slides.Rmd
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---
title: "Introduction to testing R code"
subtitle: "https://stirlingcodingclub.github.io/code_testing"
author: "Brad Duthie"
date: "22 March 2023"
output:
beamer_presentation:
theme: "default"
colortheme: "default"
fonttheme: "default"
ioslides_presentation: default
slidy_presentation: default
header-includes:
- \usepackage{hyperref}
- \usepackage{tikz}
- \usepackage{caption}
- \definecolor{links}{HTML}{2A1B81}
- \hypersetup{colorlinks,linkcolor=,urlcolor=links}
colorlinks: true
linkcolor: blue
urlcolor: blue
---
```{r, echo = FALSE}
library(knitr);
opts_chunk$set(echo = FALSE);
```
## Introduction: Why bother testing your code?
\pause
- You already do this informally (checking if a function works) \pause \newline
- Code that initially works might not later under different conditions \pause \newline
- Encourages better coding (writing shorter, more manageable functions) \pause \newline
- Reassuring to double-check that *everything* works after changing something \pause \newline
- Gratifying to watch code pass multiple automated tests (it looks cool).
## Testing all of your code at once is satisfying
<center><br>
{width=70%}
</center><br>
## Getting started: install the testthat package
Can install [testthat](https://github.com/r-lib/testthat) from [CRAN](https://cran.r-project.org/).
```{r, eval = FALSE, echo = TRUE}
install.packages("testthat")
```
**Or** install from GitHub with the [devtools](https://github.com/r-lib/devtools) R package.
```{r, eval = FALSE, echo = TRUE}
devtools::install_github("r-lib/testthat");
```
Load [testthat](https://github.com/r-lib/testthat) into Rstudio just like any other R package.
```{r, eval = TRUE, echo = TRUE}
library(testthat);
```
## Two simple functions to be tested
**Consider one [R script](https://github.com/StirlingCodingClub/SCC_R_package/blob/master/R/temp_conversion.R) (file with .R extension) with functions.**
\hrule \vspace{3 mm}
*Function 1*: converts a temperature from Fahrenheit to Celsius.
```{r, echo = TRUE}
F_to_C <- function(F_temp){
C_temp <- (F_temp - 32) * 5/9;
return(C_temp);
}
```
\pause
*Function 2*: converts from Celsius to Fahrenheit.
```{r, echo = TRUE}
C_to_F <- function(C_temp){
F_temp <- (C_temp * 9/5) + 32;
return(F_temp);
}
```
## Two simple functions to be tested
**Consider one [R script](https://github.com/StirlingCodingClub/SCC_R_package/blob/master/R/temp_conversion.R) (file with .R extension) with functions.**
\hrule \vspace{3 mm}
*Function 1*: converts a temperature from Fahrenheit to Celsius.
```{r, echo = TRUE}
F_to_C(50)
```
\pause
*Function 2*: converts from Celsius to Fahrenheit.
```{r, echo = TRUE}
C_to_F(10)
```
## How the `test_that` function works
Example of a testthat R script, < [test-temp_conversion.R](https://github.com/StirlingCodingClub/code_testing/blob/master/test-temp_conversion.R) >
```{r, echo = TRUE, eval = FALSE}
library(testthat);
context("Temperature function testing");
source("temp_conversion.R"); # Functions to test
test_that("Fahrenheit to Celsius", {
temp_C <- F_to_C(50);
# Test that the result is numeric
expect_that( is.numeric(temp_C), equals(TRUE) );
# Test that the result is the correct value
expect_that( temp_C, equals(10) );
})
```
## How to run many tests quickly
**Check Rstudio is set to the same directory as the test R script(s)**
```{r, eval = FALSE, echo = TRUE}
test_dir("."); # Runs all of your tests
```
The above will run all files with the prefix `test-` and extension `.R`.
\vspace{8 mm} \hrule \vspace{3 mm} \pause
**Test output looks like this:**
<center><br>
</center><br>
## Testing as part of your coding work flow
**Hadley Wickham also [makes several key points](http://r-pkgs.had.co.nz/tests.html) about testing**
- Helps spot bugs in the code earlier and see what needs fixing
- Multiple unit tests encourages smaller, manageable functions
- Writing failing tests can be useful when fixing bugs \pause
**Additional resources**
- [Example of unit testing R code with testthat](https://www.johndcook.com/blog/2013/06/12/example-of-unit-testing-r-code-with-testthat/) (John D. Cook)
- [Testing R packages](http://r-pkgs.had.co.nz/tests.html) (Hadley Wickam)