Add skip_if_offline

This is useful for packages which test against online APIs. We use
`curl::nslookup()` rather than `utils::nsl()` because the latter is not
available on Windows.

DESCRIPTION

@@ -27,6 +27,7 @@ Imports:
     withr (>= 2.0.0)
 Suggests: 
     covr,
+    curl (>= 0.9.5),
     devtools,
     knitr,
     rmarkdown,

NAMESPACE

@@ -124,6 +124,7 @@ export(skip)
 export(skip_if)
 export(skip_if_not)
 export(skip_if_not_installed)
+export(skip_if_offline)
 export(skip_if_translated)
 export(skip_on_appveyor)
 export(skip_on_bioc)

NEWS.md

@@ -1,5 +1,10 @@
 # testthat 2.0.0.9000
 
+## New and improved skips
+
+* `skip_if_offline()` skips tests if an internet connection is not available
+  (#685).
+
 ## Minor improvements and bug fixes
 
 * `expect_equal_to_reference` `update` parameter default value restored to

R/skip.R

@@ -14,6 +14,9 @@
 #' `skip_if_not()` works like [stopifnot()], generating
 #' a message automatically based on the first argument.
 #'
+#' `skip_if_offline()` skips tests if an internet connection is not available
+#' using [curl::nslookup()].
+#'
 #' `skip_on_cran()` skips tests on CRAN, using the `NOT_CRAN`
 #' environment variable set by devtools.
 #'
@@ -31,6 +34,7 @@
 #' a side effect, because the package is likely to be used anyway.
 #'
 #' @param message A message describing why the test was skipped.
+#' @param host A string with a hostname to lookup
 #' @export
 #' @examples
 #' if (FALSE) skip("No internet connection")
@@ -98,6 +102,16 @@ skip_if_not_installed <- function(pkg, minimum_version = NULL) {
   return(invisible(TRUE))
 }
 
+#' @export
+#' @rdname skip
+skip_if_offline <- function(host = "r-project.org") {
+  skip_if_not_installed("curl")
+  has_internet <- !is.null(curl::nslookup(host, error = FALSE))
+  if (!has_internet) {
+    skip("offline")
+  }
+}
+
 #' @export
 #' @rdname skip
 skip_on_cran <- function() {