Fix snapshots of conditions with empty lines

[gaborcsardi]

It seems to me that the simplest is to treat snapshots of conditions differently. So for these we dot remove the empty lines now.

To have a workaround that works with both testthat 3.1.1 (removing the empty lines), record your test with testthat 3.1.0 or with the fix included in this PR (will be version 3.1.1.9001) and skip them on the problematic testthat versions. E.g. something like this in a helper.R file should work:

expect_snapshot <- function(...) {
  if (packageVersion("testthat") >= "3.1.1" &&
      packageVersion("testthat") <= "3.1.1.9000") {
    skip("testthat bug with snapshots")
  }
  testthat::expect_snapshot(...)
}

Closes #1509.

[hadley]

I think my mental model of this code must be missing something because I don't understand why an empty line corresponds to character()?

[gaborcsardi]

I think it is because the message is a single \n with appendLF = FALSE (or an empty string with appendLF = TRUE) and this will end up being a character() when testthat breaks it apart into lines.

[hadley]

I think the root cause is this weirdness in strsplit():

strsplit("a\nb", "\n")[[1]]
#> [1] "a" "b"
strsplit("a\nb\n", "\n")[[1]]
#> [1] "a" "b"

strsplit("a\n", "\n")[[1]]
#> [1] "a"
strsplit("a", "\n")[[1]]
#> [1] "a"

strsplit("", "\n")[[1]]
#> character(0)
strsplit("\n", "\n")[[1]]
#> [1] ""

^{Created on 2022-01-03 by the reprex package (v2.0.1)}

So I think a slightly cleaner fix will be in snapshot_lines(). I'll do it since I'll be working on testhat for a bit.

[hadley]

Closing in favour of #1524