Executing `.onLoad()` in different test instances

[arangaca]

Consider a dummy a package foo that's intended to be used in Quarto or R Markdown. The package contains the following R script:

.onLoad <- function() print(rmarkdown::metadata$title)

I'd like to test that feature:

# helpers

local_stuff <- function(title, env = parent.frame()) {
  temp_dir <- withr::local_tempdir(.local_envir = env)
  temp_file <- withr::local_tempfile(
    lines = glue::glue("
    ---
    title: {title}
    ---
    ```{{r test}}
    library(foo)
    ```
    "),
    fileext = ".Rmd",
    tmpdir = temp_dir,
    .local_envir = env
  )
  
  rmarkdown::render(temp_file, clean = FALSE, quiet = TRUE)
  temp_dir
}

read_local_md <- function(dir) {
  file <- list.files(dir, pattern = "\\.md$", full.names = TRUE)
  cat(readr::read_file(file))
}

testthat::test_that("", {
  testthat::local_edition(3)
  
  dir <- local_stuff("bar")
  testthat::expect_snapshot(read_local_md(dir))
  
  dir <- local_stuff("baz")
  testthat::expect_snapshot(read_local_md(dir))
})
#> Can't compare snapshot to reference when testing interactively.
#> ℹ Run `devtools::test()` or `testthat::test_file()` to see changes.
#> Current value:
#> Code
#>   read_local_md(dir)
#> Output
#>   ---
#>   title: bar
#>   ---
#>   
#>   ```r
#>   library(foo)
#>   #> [1] "bar"
#>   ```
#> Can't compare snapshot to reference when testing interactively.
#> ℹ Run `devtools::test()` or `testthat::test_file()` to see changes.
#> Current value:
#> Code
#>   read_local_md(dir)
#> Output
#>   ---
#>   title: baz
#>   ---
#>   
#>   ```r
#>   library(foo)
#>   ```
#> ── Skip:  ──────────────────────────────────────────────────────────────────────
#> Reason: empty test

^{Created on 2024-02-02 by the reprex package (v2.0.1)}

As you can see, the first snapshot captures the title but not the second one, meaning that .onLoad() was executed once, when rendering for the first time.

Is there a way to unload the package from within .onLoad() when it's done with the rendering so that it could run .onLoad() in every snapshot? Defering a detach doesn't make R happy.

[Gabor]

detach() does not unload a package, unloadNamespace() does, but it does not seem like a good idea to me.

To test things that happen during loading, load the package in a subprocess, and then check the output:

callr::r(function() loadNamespace(...))

[arangaca]

How would you use it in my example? Would you replace lines with:

glue::glue("
  ---
  title: {title}
  ---
  ```{{r test}}
  foo <- callr::r(function() loadNamespace('foo'))
  foo$.onLoad()
  ```
")

[Gabor]

It does not have to be in an Rmd for testing:

❯ callr::r(function() library(tidyverse), stdout = tmp <- tempfile(), stderr = "2>&1")
❯ readLines(tmp)
 [1] "── Attaching core tidyverse packages ──────────────────────── tidyverse 2.0.0 ──"
 [2] "✔ dplyr     1.1.4     ✔ readr     2.1.4"
 [3] "✔ forcats   1.0.0     ✔ stringr   1.5.1"
 [4] "✔ ggplot2   3.4.4     ✔ tibble    3.2.1"
 [5] "✔ lubridate 1.9.3     ✔ tidyr     1.3.0"
 [6] "✔ purrr     1.0.2     "
 [7] "── Conflicts ────────────────────────────────────────── tidyverse_conflicts() ──"
 [8] "✖ dplyr::filter() masks stats::filter()"
 [9] "✖ dplyr::lag()    masks stats::lag()"
[10] "ℹ Use the conflicted package (<http://conflicted.r-lib.org/>) to force all conflicts to become errors"

But if you really want to put it in an .Rmd, you can do that as well, and call knit() from a subprocess.