Improve errors when a non-vector is passed to expect_vector. (#2229)

The `expect_vector` function delegates most of its logic to
`vctrs::vec_assert`, which can throw one of two errors,
`vctrs_error_assert` and `vctrs_error_scalar_type`.

Only the former one was being handled, not the latter. This doesn't
affect the behaviour of tests much, but it produces sub-par error
messages and causes failing tests to terminate immediately rather than
recording the error and continuing like other assertions do.

---------

Co-authored-by: Hadley Wickham <[email protected]>

Author: plietar

NEWS.md

@@ -1,5 +1,6 @@
 # testthat (development version)
 
+* `expect_vector()` fails, instead of erroring, if `object` is not a vector (@plietar, #2224).
 * New `vignette("mocking")` explains mocking in detail (#1265).
 * New `vignette("challenging-functions")` provides an index to other documentation organised by testing challenges (#1265).
 * When running a test interactively, testthat now reports the number of succeses. The results should also be more useful if you are using nested tests.

R/expect-vector.R

@@ -17,19 +17,20 @@
 expect_vector <- function(object, ptype = NULL, size = NULL) {
   check_installed("vctrs")
   check_number_whole(size, min = 0, allow_null = TRUE)
-
   act <- quasi_label(enquo(object))
+  # vec_assert() automatically adds backticks so we hack out the ones
+  # added by as_label()
+  act$lab <- gsub("^`|`$", "", act$lab)
 
-  message <- NULL
-  tryCatch(
+  withCallingHandlers(
     vctrs::vec_assert(act$val, ptype = ptype, size = size, arg = act$lab),
+    vctrs_error_scalar_type = function(e) {
+      fail(e$message)
+    },
     vctrs_error_assert = function(e) {
-      message <<- e$message
+      fail(e$message)
     }
   )
 
-  if (!is.null(message)) {
-    return(fail(message))
-  }
   pass(act$val)
 }

tests/testthat/_snaps/expect-vector.md

@@ -1,3 +1,19 @@
+# basic properties upheld
+
+    Code
+      expect_vector(x, size = 5)
+    Condition
+      Error:
+      ! `x` must have size 5, not size 10.
+
+---
+
+    Code
+      expect_vector(y)
+    Condition
+      Error:
+      ! `y` must be a vector, not `NULL`.
+
 # expect_vector validates its inputs
 
     Code

tests/testthat/test-expect-vector.R

@@ -2,7 +2,12 @@ test_that("basic properties upheld", {
   skip_if_not_installed("vctrs", "0.1.0.9002")
 
   expect_success(expect_vector(1:10, size = 10))
-  expect_failure(expect_vector(1:10, size = 5))
+
+  x <- 1:10
+  expect_snapshot_failure(expect_vector(x, size = 5))
+
+  y <- NULL
+  expect_snapshot_failure(expect_vector(y))
 })
 
 test_that("expect_vector validates its inputs", {