Add test for failure message

Author: hadley

tests/testthat/_snaps/expect-shape.md

@@ -1,3 +1,7 @@
+# generates actionable failure message
+
+    `x` has length 10, not length 2.
+
 # expect_length validates its inputs
 
     Code

tests/testthat/test-expect-shape.R

@@ -1,10 +1,15 @@
 test_that("length computed correctly", {
   expect_success(expect_length(1, 1))
-  expect_failure(expect_length(1, 2), "has length 1, not length 2.")
   expect_success(expect_length(1:10, 10))
   expect_success(expect_length(letters[1:5], 5))
 })
 
+test_that("generates actionable failure message", {
+  x <- 1:10
+  expect_snapshot_failure(expect_length(x, 2))
+  expect_length(x, 15)
+})
+
 test_that("uses S4 length method", {
   A <- setClass("ExpectLengthA", slots = c(x = "numeric", y = "numeric"))
   setMethod("length", "ExpectLengthA", function(x) 5L)