Preserve empty lines in snapshot output (#1524)

Fixes #1509.

Author: hadley

NEWS.md

@@ -1,5 +1,8 @@
 # testthat (development version)
 
+* `expect_snapshot()` no longer inadvertently trims trailing new lines off
+  of errors and messages (#1509).
+
 * `test_that()` no longer inappropriately skips when calling `expect_equal()`
   when you've temporarily set the locale to non-UTF-8 (#1285).
 

R/snapshot.R

@@ -160,16 +160,18 @@ snapshot_replay.condition <- function(x,
   c(snap_header(state, type), snapshot_lines(msg, transform))
 }
 
-snapshot_replay_condition_legacy <- function(x, state, transform = NULL) {
+snapshot_replay_condition_legacy <- function(x, state = env(), transform = NULL) {
   msg <- cnd_message(x)
+
   if (inherits(x, "error")) {
     state$error <- x
     type <- "Error"
+    msg <- add_implict_nl(msg)
   } else if (inherits(x, "warning")) {
     type <- "Warning"
+    msg <- paste0(msg, "\n")
   } else if (inherits(x, "message")) {
     type <- "Message"
-    msg <- sub("\n$", "", msg)
   } else {
     type <- "Condition"
   }
@@ -188,6 +190,14 @@ snapshot_lines <- function(x, transform = NULL) {
   x
 }
 
+add_implict_nl <- function(x) {
+  if (substr(x, nchar(x), nchar(x)) == "\n") {
+    x
+  } else {
+    paste0(x, "\n")
+  }
+}
+
 snap_header <- function(state, header) {
   if (!identical(state$header, header)) {
     state$header <- header

tests/testthat/_snaps/snapshot.md

@@ -27,6 +27,23 @@
     Error <simpleError>
       4
 
+# empty lines are preserved
+
+    Code
+      f()
+    Output
+      1
+      
+    Message <simpleMessage>
+      2
+      
+    Warning <simpleWarning>
+      3
+      
+    Error <simpleError>
+      4
+      
+
 # multiple outputs of same type are collapsed
 
     Code

tests/testthat/test-snapshot.R

@@ -20,6 +20,16 @@ test_that("can snapshot everything", {
   expect_snapshot(f(), error = TRUE)
 })
 
+test_that("empty lines are preserved", {
+  f <- function() {
+    cat("1\n\n")
+    message("2\n")
+    warning("3\n")
+    stop("4\n\n")
+  }
+  expect_snapshot(f(), error = TRUE)
+})
+
 test_that("multiple outputs of same type are collapsed", {
   expect_snapshot({
     x <- 1