Check expect() and fail() inputs (#2254)

Fixes #2247

Author: hadley

R/expect-that.R

@@ -8,8 +8,9 @@
 #' Learn more about creating your own expectations in
 #' `vignette("custom-expectation")`.
 #'
-#' @param message Failure message to send to the user. It's best practice to
-#'   describe both what is expected and what was actually received.
+#' @param message A character vector describing the failure. The
+#'   first element should describe the expected value, and the second (and
+#'   optionally subsequence) elements should describe what was actually seen.
 #' @param info Character vector continuing additional information. Included
 #'   for backward compatibility only and new expectations should not use it.
 #' @param srcref Location of the failure. Should only needed to be explicitly
@@ -41,6 +42,9 @@ fail <- function(
   trace_env = caller_env(),
   trace = NULL
 ) {
+  check_character(message)
+  check_character(info, allow_null = TRUE)
+
   trace <- trace %||% capture_trace(trace_env)
   message <- paste(c(message, info), collapse = "\n")
   expectation("failure", message, srcref = srcref, trace = trace)

R/expectation.R

@@ -5,7 +5,9 @@
 #' `vignette("custom-expectation")` for details.
 #'
 #' @param ok `TRUE` or `FALSE` indicating if the expectation was successful.
-#' @param failure_message Message to show if the expectation failed.
+#' @param failure_message A character vector describing the failure. The
+#'   first element should describe the expected value, and the second (and
+#'   optionally subsequence) elements should describe what was actually seen.
 #' @inheritParams fail
 #' @return An expectation object from either `succeed()` or `fail()`.
 #'   with a `continue_test` restart.
@@ -20,6 +22,9 @@ expect <- function(
   trace = NULL,
   trace_env = caller_env()
 ) {
+  check_bool(ok)
+  check_character(failure_message)
+
   if (!ok) {
     return(fail(
       failure_message,

man/expect.Rd

@@ -0,0 +1,13 @@
+# validates key inputs
+
+    Code
+      expect(1)
+    Condition
+      Error in `expect()`:
+      ! `ok` must be `TRUE` or `FALSE`, not the number 1.
+    Code
+      expect(TRUE, 1)
+    Condition
+      Error in `expect()`:
+      ! `failure_message` must be a character vector, not the number 1.
+

man/fail.Rd

@@ -7,6 +7,13 @@ test_that("info only evaluated on failure", {
   expect_no_error(expect(TRUE, "fail", info = stop("!")))
 })
 
+test_that("validates key inputs", {
+  expect_snapshot(error = TRUE, {
+    expect(1)
+    expect(TRUE, 1)
+  })
+})
+
 test_that("can subclass expectation", {
   exp <- new_expectation(
     "failure",