Skipping tests

Sometimes you have tests that you can’t or don’t want to run in certain circumstances. This vignette describes how to skip tests to avoid execution in undesired environments. The most common scenarios are:

You’re testing a web service that occasionally fails, and you don’t want to run the tests on CRAN. Or the API requires authentication, and you can only run the tests when you’ve securely distributed secrets.
You’re relying on features that not all operating systems possess, and want to make sure your code doesn’t run on platforms where it doesn’t work. The most common platform with limitations is Windows, which among other things lacks full UTF-8 support.
You’re writing tests for multiple versions of R or multiple versions of a dependency, and you want to skip when a feature isn’t available. You generally don’t need to skip tests if a suggested package is not installed. This is only needed in exceptional circumstances, e.g., when a package is not available on some operating systems.

library(testthat)

Basics

testthat comes with a variety of helpers for the most common situations:

skip_if_not_installed() skips if a required package is not installed. You can optionally supply a minimal version too.
skip_on_cran() skips tests on CRAN. skip_on_bioc() skips tests on Bioconductor. This is useful for slow tests and tests that occasionally fail for reasons outside of your control.
skip_on_os() allows you to skip tests on a specific operating system. Generally, you should strive to avoid this as much as possible (so your code works the same on all platforms), but sometimes it’s just not possible.
skip_on_ci() skips tests on most CI platforms (e.g., GitHub Actions).
skip_on_covr() skips tests during code coverage.
skip_unless_r(">= 4.2") only runs tests for newer R versions. skip_unless_r("< 4.2") only runs tests for older R versions.

You can implement your own using skips skip_if() or skip_if_not():

# Only run test if a token file is available
skip_if_not(file.exists("secure-token.json"))

# Only run test if R has memory profiling capabilities
skip_if_not(capabilities("profmem"))

# Only run if we've opted-in to slow tests with an env var
skip_if(Sys.getenv("RUN_SLOW_TESTS") == "true")

All reporters show which tests are skipped. As of testthat 3.0.0, ProgressReporter (used interactively) and CheckReporter (used inside R CMD check) also display a summary of skips across all tests. It looks something like this:

── Skipped tests  ───────────────────────────────────────────────────────
● No token (3)
● On CRAN (1)

This display is really important, and you should keep an eye on it when working on your test suite. If you accidentally skip too many tests, you can trick yourself into believing your code is working correctly, when actually you’re just not testing it.

Helpers

If you find yourself using the same skip_if() or skip_if_not() expression across multiple tests, it’s a good idea to create a helper function. This function should start with skip_ and live in a tests/testthat/helper-{something}.R file:

skip_if_dangerous <- function() {
  if (!identical(Sys.getenv("DANGER"), "")) {
    skip("Not run in dangerous environments.")
  } else {
    invisible()
  }
}

Embedding `skip()` in package functions

Another useful technique is to embed a skip() directly into a package function. For example, take a look at pkgdown:::convert_markdown_to_html(), which absolutely cannot work if the Pandoc tool is unavailable:

convert_markdown_to_html <- function(in_path, out_path, ...) {
  if (rmarkdown::pandoc_available("2.0")) {
    from <- "markdown+gfm_auto_identifiers-citations+emoji+autolink_bare_uris"
  } else if (rmarkdown::pandoc_available("1.12.3")) {
    from <- "markdown_github-hard_line_breaks+tex_math_dollars+tex_math_single_backslash+header_attributes"
  } else {
    if (is_testing()) {
      testthat::skip("Pandoc not available")
    } else {
      abort("Pandoc not available")
    }
  }
  
  ...
}

If Pandoc is not available when convert_markdown_to_html() executes, it throws an error unless it appears to be part of a test run, in which case the test is skipped. This is an alternative to implementing a custom skipper, e.g., skip_if_no_pandoc(), and inserting it into many of pkgdown’s tests.

We don’t want pkgdown to have a runtime dependency on testthat, so pkgdown includes a copy of testthat::is_testing():

is_testing <- function() {
  identical(Sys.getenv("TESTTHAT"), "true")
}

It might look like the code still has a runtime dependency on testthat, because of the call to testthat::skip(). But testthat::skip() is only executed during a test run, which means that testthat is installed.

We have mixed feelings about this approach. On the one hand, it feels elegant and concise, and it absolutely guarantees that you’ll never miss a needed skip in one of your tests. On the other hand, it mixes code and tests in an unusual way, and when you’re focused on the tests, it’s easy to miss the fact that a package function contains a skip().

Basics

Helpers

Embedding skip() in package functions

Embedding `skip()` in package functions