Skipping tests

knitr::opts_chunk$set(
  collapse = TRUE,
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)

Some times you have tests that you don't want to run in certain circumstances. This vignette describes how to skip tests to avoid execution in undesired environments. Skipping is a relatively advanced topic because in most cases you want all your tests to run everywhere. The most common exceptions are:

library(testthat)

Basics

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

You can also easily implement your own using either skip_if() or skip_if_not(), which both take an expression that should yield a single TRUE or FALSE.

All reporters show which tests as skipped. As of testthat 3.0.0, ProgressReporter (used interactively) and CheckReporter (used inside of 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)

You should keep an on eye this when developing interactively to make sure that you're not accidentally skipping the wrong things.

Helpers

If you find yourself using the same skip_if()/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 somewhere in your R/ directory.

skip_if_Tuesday <- function() {
  if (as.POSIXlt(Sys.Date())$wday != 2) {
    return(invisible(TRUE))
  }

  skip("Not run on Tuesday")
}

It's important to test your skip helpers because it's easy to miss if you're skipping more often than desired, and the test code is never run. This is unlikely to happen locally (since you'll see the skipped tests in the summary), but is quite possible in continuous integration.

For that reason, it's a good idea to add a test that you skip is activated when you expect. skips are a special type of condition, so you can test for their presence/absence with expect_condition(). For example, imagine that you've defined a custom skipper that skips tests whenever an environment variable DANGER is set:

skip_if_dangerous <- function() {
  if (identical(Sys.getenv("DANGER"), "")) {
    return(invisible(TRUE))
  }

  skip("Not run in dangerous enviromnents")
}

Then you can use expect_condition() to test that it skips tests when it should, and doesn't skip when it shouldn't:

test_that("skip_if_dangerous work", {
  # Test that a skip happens
  withr::local_envvar(DANGER = "yes")
  expect_condition(skip_if_dangerous(), class = "skip") 

  # Test that a skip doesn't happen
  withr::local_envvar(DANGER = "")
  expect_condition(skip_if_dangerous(), NA, class = "skip")
})

Testing skip_if_Tuesday() is harder because there's no way to control the skipping from the outside. That means you'd need to "mock" its behaviour in a test, using the mockery or mockr packages.



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testthat documentation built on Oct. 4, 2021, 9:07 a.m.