test/old: do not special-case test_autochdir

Use "CheckFunction" for standard error message
for missing "test_autochdir()".

Sync test_autochdir.vim to the latest Vim commit
because porting Vim patches for this file
modify other files and are too tedious to port.

src/nvim/testdir/Makefile

@@ -36,13 +36,11 @@ NEW_TESTS_IN_ALOT := $(shell sed -n '/^source/ s/^source //; s/\.vim$$//p' $(add
 NEW_TESTS_IN_ALOT_LATIN := $(shell sed -n '/^source/ s/^source //; s/\.vim$$//p' test_alot_latin.vim)
 # Ignored tests.
 # test_alot_latin: Nvim does not allow setting encoding.
-# test_autochdir: ported to Lua, but kept for easier merging.
 # test_eval_func: used as include in old-style test (test_eval.in).
 # test_listlbr: Nvim does not allow setting encoding.
 # test_largefile: uses too much resources to run on CI.
 NEW_TESTS_IGNORE := \
   test_alot_latin $(NEW_TESTS_IN_ALOT_LATIN) \
-  test_autochdir \
   test_eval_func \
   test_listlbr \
   test_largefile \

src/nvim/testdir/test_autochdir.vim

@@ -1,10 +1,10 @@
 " Test 'autochdir' behavior
 
-if !exists("+autochdir")
-  throw 'Skipped: autochdir feature missing'
-endif
+source check.vim
+CheckOption autochdir
 
 func Test_set_filename()
+  CheckFunction test_autochdir
   let cwd = getcwd()
   call test_autochdir()
   set acd
@@ -17,3 +17,5 @@ func Test_set_filename()
   exe 'cd ' . cwd
   call delete('samples/Xtest')
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab