patch 8.2.0615: regexp benchmark stest is old style

Problem:    Regexp benchmark stest is old style.
Solution:   Make it a new style test.  Fix using a NULL list.  Add more tests.
            (Yegappan Lakshmanan, closes #5963)
diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index a8648f8..b7a523e 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -299,6 +299,8 @@
   redir END
   call assert_true(match(res, "W19:") < 0)
   au! VimEnter
+
+  call assert_fails('augroup!', 'E471:')
 endfunc
 
 func Test_BufReadCmdHelp()