Decouple edition setting in capture vs expect_snapshot()

This is appears to be some sort of change in behaviour in withr 2.5.0 vs 3.0.0.

The key point is to capture the checklist with testthat 2e in force, while still being able to execute expect_snapshot(), which requires testhat 3e.

The changes around the DESCRIPTION file in the test package are separate and are just about making it look more like the DESCRIPTION file of a package who hasn't updated to testthat 3e.

tests/testthat/_snaps/upkeep.md

@@ -85,8 +85,7 @@
 ---
 
     Code
-      local_edition(2L)
-      writeLines(upkeep_checklist())
+      writeLines(checklist)
     Output
       * [ ] `usethis::use_readme_rmd()`
       * [ ] `usethis::use_github_links()`

tests/testthat/test-upkeep.R

@@ -26,16 +26,26 @@ test_that("upkeep bullets don't change accidentally",{
 
   expect_snapshot(writeLines(upkeep_checklist()))
 
-  # Add some files to test conditional todos
+  # Test some conditional TODOs
   use_code_of_conduct("jane.doe@foofymail.com")
-  use_testthat()
   writeLines("# test environment\n", "cran-comments.md")
   local_mocked_bindings(git_default_branch = function() "master")
 
-  expect_snapshot({
+  # Look like a package that hasn't switched to testthat 3e yet
+  use_testthat()
+  desc::desc_del("Config/testthat/edition")
+  desc::desc_del("Suggests")
+  use_package("testthat", "Suggests")
+
+  # previously (withr 2.5.0) we could put local_edition(2L) inside {..} inside
+  # the expect_snapshot() call
+  # that is no longer true with withr 3.0.0, but this hacktastic approach works
+  local({
     local_edition(2L)
-    writeLines(upkeep_checklist())
+    checklist <<- upkeep_checklist()
   })
+
+  expect_snapshot(writeLines(checklist))
 })
 
 test_that("get extra upkeep bullets works", {