make skip if not functions

NAMESPACE

@@ -1,6 +1,7 @@
 # Generated by roxygen2: do not edit by hand
 
 export(is_installed2)
+export(make_skip_if_not_function)
 export(opt_set_local2)
 export(source_pef)
 export(transform_with_generated)

R/tests.R

@@ -2,7 +2,7 @@
 #'
 #' To be used as an argument for [testthat::expect_snapshot()].
 #' @param x A character vector.
-#' @keywords snapshot helpers
+#' @keywords snapshot helpers, testing helpers
 #' @name transform_snap
 NULL
 
@@ -16,3 +16,45 @@ transform_with_generated <- function(x = character()) {
     x
   )
 }
+
+#' Make a [testthat::skip_if_not()] function
+#'
+#' Function operator to turn
+#' [checkmate](https://mllg.github.io/checkmate/index.html)'s
+#' `check_*()`-type functions into [testthat](https://testthat.r-lib.org)'s
+#' `skip_if_not_*()` functions.
+#'
+#' @inheritParams checkmate::makeAssertionFunction
+#' @details
+#' Notice that `check_*()` are always formulated *positively*;
+#' the message from `check_*()` is emitted,
+#' when its condition is *not* met.
+#' The [testthat](https://testthat.r-lib.org) equivalent is the opposite:
+#' a `skip_if_not_*()` function would skip with the emitted message.
+#'
+#' You cannot generate `skip_if_*()` functions from `check_*()` functions,
+#' because the negation of the emitted message may be wrong or confusing.
+#' But you can create one manually:
+#'
+#' ```r
+#' skip_if_cond <- function(x) {
+#'   testthat::skip_if(
+#'     my_pkg::check_cond(x),
+#'     # needs a custom message here
+#'     "Skipping because condition is true."
+#'   )
+#' }
+#' ```
+#' @export
+#' @keywords testing helpers
+make_skip_if_not_function <- function(check.fun) {
+  force(check.fun)
+  function(...) {
+    res <- check.fun(...)
+    if (isTRUE(res)) {
+      return(invisible())
+    } else {
+      testthat::skip(res)
+    }
+  }
+}

tests/testthat/test-tests.R

@@ -0,0 +1,9 @@
+describe("make_skip_if_not_function", {
+  it("returns invisibly if success", {
+    expect_equal(
+      make_skip_if_not_function(checkmate::check_scalar)(1),
+      invisible()
+    )
+  })
+  # can't easily test for failure, because then it would, well, skip.
+})