✨ Don't lose last snapshot if last nl is missing ✨ (#2164)

Because positron (and other editors) have an edit of trimming additional trailing newlines when saving. It probably would have been better to not write this in the first place, but I think we don't want to change that now as it will cause diffs to all snapshots, and only protects against a problem that happens rarely.

Fixes #2092

Author: hadley

.claude/settings.local.json

@@ -1,10 +1,12 @@
 {
+  "$schema": "https://json.schemastore.org/claude-code-settings.json",
   "permissions": {
     "allow": [
       "Bash(find:*)",
-      "Bash(R:*)"
+      "Bash(R:*)",
+      "Bash(rm:*)",
+      "Bash(air format:*)"
     ],
     "deny": []
-  },
-  "$schema": "https://json.schemastore.org/claude-code-settings.json"
+  }
 }

NEWS.md

@@ -1,5 +1,6 @@
 # testthat (development version)
 
+* The last snapshot is no longer lost if the snapshot file is missing the final newline (#2092). It's easy to accidentally remove this because there are two trailing new lines in snapshot files and many editors will automatically remove if you touch the file.
 * New `expect_r6_class()` (#2030).
 * `expect_*()` functions consistently and rigorously check their inputs (#1754). 
 * `JunitReporter()` no longer fails with `"no applicable method for xml_add_child"` for warnings outside of tests (#1913). Additionally, warnings now save their backtraces.

R/snapshot-serialize.R

@@ -19,9 +19,13 @@ snap_from_md <- function(lines) {
     sep <- grepl("^-{3,}", lines)
     case_group <- cumsum(sep)
 
-    # Remove first line and last line, separator, line above and line below
+    # Remove first line, separator, line above and line below
+    # Only remove last line if it's empty (to handle missing final newlines)
     sep_loc <- which(sep)
-    drop <- c(1, sep_loc, sep_loc + 1, sep_loc - 1, length(lines))
+    drop <- c(1, sep_loc, sep_loc + 1, sep_loc - 1)
+    if (length(lines) > 0 && lines[length(lines)] == "") {
+      drop <- c(drop, length(lines))
+    }
 
     cases <- unname(split(lines[-drop], case_group[-drop]))
     code_unblock <- function(x) paste0(indent_del(x), collapse = "\n")

tests/testthat/test-snapshot-serialize.R

@@ -25,3 +25,22 @@ test_that("snapshots always use \n", {
   has_cr <- grepl("\r", snap, fixed = TRUE)
   expect_equal(has_cr, FALSE)
 })
+
+test_that("snap_from_md handles missing final newlines", {
+  one_newline <- withr::local_tempfile(
+    fileext = ".md",
+    lines = c(
+      "# test_case",
+      "",
+      "result1",
+      "",
+      "---",
+      "",
+      "result2"
+    )
+  )
+  expect_equal(
+    read_snaps(one_newline),
+    list(test_case = c("result1", "result2"))
+  )
+})