Make require_testthat helper function

NEWS.md

@@ -56,6 +56,7 @@
 * `make_linter_from_xpath()` errors up front when `lint_message` is missing (instead of delaying this error until the linter is used, #2541, @MichaelChirico).
 * `paste_linter()` is extended to recommend using `paste()` instead of `paste0()` for simply aggregating a character vector with `collapse=`, i.e., when `sep=` is irrelevant (#1108, @MichaelChirico).
 * `expect_no_lint()` was added as new function to cover the typical use case of expecting no lint message, akin to the recent {testthat} functions like `expect_no_warning()` (#2580, @F-Noelle).
+* `expect_lint_free()` and other functions that rely on the {testthat} framework now have a consistent error message. (#2585, @F-Noelle).
 
 ### New linters
 

R/expect_lint.R

@@ -42,13 +42,8 @@
 #' )
 #' @export
 expect_lint <- function(content, checks, ..., file = NULL, language = "en") {
-  if (!requireNamespace("testthat", quietly = TRUE)) {
-    stop( # nocov start
-      "'expect_lint' and 'expect_no_lint' are designed to work within the 'testthat' testing framework, ",
-      "but 'testthat' is not installed.",
-      call. = FALSE
-    ) # nocov end
-  }
+  require_testthat("expect_lint")
+
   old_lang <- set_lang(language)
   on.exit(reset_lang(old_lang))
 
@@ -129,18 +124,20 @@ expect_lint <- function(content, checks, ..., file = NULL, language = "en") {
 #' @rdname expect_lint
 #' @export
 expect_no_lint <- function(content, ..., file = NULL, language = "en") {
+  require_testthat("expect_no_lint")
   expect_lint(content, NULL, ..., file = file, language = language)
 }
 
 #' Test that the package is lint free
 #'
-#' This function is a thin wrapper around lint_package that simply tests there are no
-#' lints in the package.  It can be used to ensure that your tests fail if the package
-#' contains lints.
+#' This function is a thin wrapper around lint_package that simply tests there are no lints in the package.
+#' It can be used to ensure that your tests fail if the package contains lints.
 #'
 #' @param ... arguments passed to [lint_package()]
 #' @export
 expect_lint_free <- function(...) {
+  require_testthat("expect_lint_free")
+
   testthat::skip_on_cran()
   testthat::skip_on_covr()
 
@@ -158,3 +155,13 @@ expect_lint_free <- function(...) {
 
   invisible(result)
 }
+
+# Helper function to check if testthat is installed.
+require_testthat <- function(name) {
+  if (!requireNamespace("testthat", quietly = TRUE)) {
+    stop( # nocov start
+      name, "is designed to work within the 'testthat' testing framework, but 'testthat' is not installed.",
+      call. = FALSE
+    ) # nocov end
+  }
+}