Date: 2020-03-10

# One function at a time

#### 2020-03-10

This vignette will teach you how to create a unit test shell for the examples in a single function’s documentation.

## Setup

First, let’s set up a dummy package called `tempkg` with just the `detect.R` and `match.R` files from the source code of the `stringr` package.

    usethis::create_package("tempkg", open = FALSE)
    fs::file_copy(
      system.file("extdata", c("detect.R", "match.R"), package = "exampletestr"),
      "tempkg/R/"
    )

Now let’s move into the `tempkg` directory:

    setwd("tempkg/")

and set the active project:

    usethis::proj_set(".")

    #> ✔ Setting active project to '/private/var/folders/l_/2mwm03p55zg7zjykv084hhvr0000gn/T/RtmpPdOSWX/tempkg'

# Main event

The `detect.R` file looks like this (well, I’ve abbreviated it slightly):

    #' Detect the presence or absence of a pattern in a string.
    #'
    #' Vectorised over `string` and `pattern`.
    #'
    #' @param string Input vector. Either a character vector, or something
    #'  coercible to one.
    #' @param pattern Pattern to look for.
    #'
    #' @return A logical vector.
    #'
    #' @export
    #' @examples
    #' fruit <- c("apple", "banana", "pear", "pinapple")
    #' str_detect(fruit, "a")
    #' str_detect(fruit, "^a")
    #' str_detect(fruit, "a$")
    #' str_detect(fruit, "b")
    #' str_detect(fruit, "[aeiou]")
    str_detect <- function(string, pattern) {
      switch(type(pattern),
        empty = ,
        bound = str_count(string, pattern) > 0,
        fixed = stri_detect_fixed(string, pattern, opts_fixed = opts(pattern)),
        coll = stri_detect_coll(string, pattern, opts_collator = opts(pattern)),
        regex = stri_detect_regex(string, pattern, opts_regex = opts(pattern))
      )
    }

We can make the unit tests shell file for the `str_match()` function using `make_test_shell_fun()`:

    make_test_shell_fun("str_detect", open = FALSE)

This outputs a `test-str_detect-examples.R` file in the `tests/testthat` folder with contents

    test_that("`str_detect()` works", {
      fruit <- c("apple", "banana", "pear", "pinapple")
      expect_equal(str_detect(fruit, "a"), )
      expect_equal(str_detect(fruit, "^a"), )
      expect_equal(str_detect(fruit, "a$"), )
      expect_equal(str_detect(fruit, "b"), )
      expect_equal(str_detect(fruit, "[aeiou]"), )
      expect_equal(str_detect("aecfg", letters), )
    })

which can be sensibly completed as

    test_that("`str_detect()` works", {
      fruit <- c("apple", "banana", "pear", "pinapple")
      expect_equal(str_detect(fruit, "a"), rep(TRUE, 4))
      expect_equal(str_detect(fruit, "^a"), c(TRUE, rep(FALSE, 3)))
      expect_equal(str_detect(fruit, "a$"), c(FALSE, TRUE, FALSE, FALSE))
      expect_equal(str_detect(fruit, "b"), c(FALSE, TRUE, FALSE, FALSE))
      expect_equal(str_detect(fruit, "[aeiou]"), rep(TRUE, 4))
      expect_equal(
        str_detect("aecfg", letters),
        letters %in% c("a", "c", "e", "f", "g")
      )
    })

# Roxytest functionality

Alternatively, we can use the `roxytest` (https://github.com/mikldk/roxytest) package’s `@testexamples` roxygen tag for testing examples.

    make_test_shell_fun("str_detect", roxytest = TRUE)

    #> ℹ Running `roxygen2::roxygenize` . . .

    #> Updating roxygen version in /private/var/folders/l_/2mwm03p55zg7zjykv084hhvr0000gn/T/RtmpPdOSWX/tempkg/DESCRIPTION

    #> Loading tempkg

    #> ✔ Roxygenized :-)
    #>   @testexamples
    #>   #' expect_equal(str_detect(fruit, "a"), )
    #>   #' expect_equal(str_detect(fruit, "^a"), )
    #>   #' expect_equal(str_detect(fruit, "a$"), )
    #>   #' expect_equal(str_detect(fruit, "b"), )
    #>   #' expect_equal(str_detect(fruit, "[aeiou]"), )
    #>   #' expect_equal(str_detect("aecfg", letters), )
    #>   [Copied to clipboard]
    #> ● Paste the block into your roxygen documentation.
    #> ● Complete the tests in the block.
    #> ● Run `devtools::document()` to generate the tests in 'tests/'.

## RStudio addin for roxytest functionality

This can also be done by highlighting the function name and selecting the RStudio addin Copy roxytest @testexamples to clipboard.

# Cleanup

    knitr::opts_knit$set(root.dir = tempdir(check = TRUE))

    if (fs::dir_exists("tempkg")) fs::dir_delete("tempkg")
    knitr::opts_knit$set(root.dir = init_wd)