Automatically skip missing packages on CRAN (#2173)

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()` now automatically skips 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.)
 * `expect_snapshot()` no longer skips on CRAN, as that skips the rest of the test. Instead it just returns, neither succeeding nor failing (#1585).
 * Interrupting a test now prints the test name. This makes it easier to tell where a very slow test might be hanging (#1464)
 * Parallel testthat now does not ignore test files with syntax errors (#1360).

R/test-that.R

@@ -173,6 +173,11 @@ 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")
+})