Automatically skip missing packages on CRAN

Practically, this should mean that you never need to add `skip_if_not_installed()` for suggested packages. It's already the tidyverse style to not do this, but now this works everywhere.

Fixes #1585

Author: hadley

NEWS.md

@@ -1,5 +1,6 @@
 # testthat (development version)
 
+* On CRAN, `test_that()` will now automatically skip if a package is not installed (#1585). Practically, this means that you no longer need to check that suggested packages are installed. (We don't do this in the tidyverse because we think it has limited payoff, but other styles advise differently.)
 * Parallel testthat now does not ignore test files with syntax errors (#1360).
 * `expect_lt()`, `expect_gt()`, and friends have a refined display that is more likely to display the correct number of digits and shows you the actual values compared.
 * `describe()`, `it()`, and `test_that()` now have a shared stack of descriptions so that if you nest any inside of each other, any resulting failures will show you the full path.

R/test-that.R

@@ -167,6 +167,11 @@ test_code <- function(code, env, reporter = NULL, skip_on_empty = TRUE) {
           }
         },
         expectation = handle_expectation,
+        packageNotFoundError = function(e) {
+          if (on_cran()) {
+            skip(paste0(e$package, " is not installed."))
+          }
+        },
         skip = handle_skip,
         warning = handle_warning,
         message = handle_message,

tests/testthat/test-test-that.R

@@ -147,3 +147,20 @@ test_that("no braces required in testthat 2e", {
     NA
   )
 })
+
+test_that("missing packages cause a skip on CRAN", {
+  local_on_cran(TRUE)
+
+  expectations <- capture_expectations(test_that("", {
+    library(notinstalled)
+  }))
+  expect_length(expectations, 1)
+  expect_s3_class(expectations[[1]], "expectation_skip")
+
+  local_on_cran(FALSE)
+  expectations <- capture_expectations(test_that("", {
+    library(notinstalled)
+  }))
+  expect_length(expectations, 1)
+  expect_s3_class(expectations[[1]], "expectation_error")
+})