patch 8.1.1331: test 29 is old style

Problem:    Test 29 is old style.
Solution:   Turn it into a new style test. (Yegappan Lakshmanan, closes #4370)
diff --git a/src/testdir/test_backspace_opt.vim b/src/testdir/test_backspace_opt.vim
index fd81f42..e6ea0bc 100644
--- a/src/testdir/test_backspace_opt.vim
+++ b/src/testdir/test_backspace_opt.vim
@@ -56,4 +56,55 @@
   set nocompatible viminfo+=nviminfo
 endfunc
 
+" Test with backspace set to the non-compatible setting
+func Test_backspace_ctrl_u()
+  new
+  call append(0,  [
+        \ "1 this shouldn't be deleted",
+        \ "2 this shouldn't be deleted",
+        \ "3 this shouldn't be deleted",
+        \ "4 this should be deleted",
+        \ "5 this shouldn't be deleted",
+        \ "6 this shouldn't be deleted",
+        \ "7 this shouldn't be deleted",
+        \ "8 this shouldn't be deleted (not touched yet)"])
+  call cursor(2, 1)
+
+  set compatible
+  set backspace=2
+
+  exe "normal Avim1\<C-U>\<Esc>\<CR>"
+  exe "normal Avim2\<C-G>u\<C-U>\<Esc>\<CR>"
+
+  set cpo-=<
+  inoremap <c-u> <left><c-u>
+  exe "normal Avim3\<C-U>\<Esc>\<CR>"
+  iunmap <c-u>
+  exe "normal Avim4\<C-U>\<C-U>\<Esc>\<CR>"
+
+  " Test with backspace set to the compatible setting
+  set backspace= visualbell
+  exe "normal A vim5\<Esc>A\<C-U>\<C-U>\<Esc>\<CR>"
+  exe "normal A vim6\<Esc>Azwei\<C-G>u\<C-U>\<Esc>\<CR>"
+
+  inoremap <c-u> <left><c-u>
+  exe "normal A vim7\<C-U>\<C-U>\<Esc>\<CR>"
+
+  call assert_equal([
+        \ "1 this shouldn't be deleted",
+        \ "2 this shouldn't be deleted",
+        \ "3 this shouldn't be deleted",
+        \ "4 this should be deleted3",
+        \ "",
+        \ "6 this shouldn't be deleted vim5",
+        \ "7 this shouldn't be deleted vim6",
+        \ "8 this shouldn't be deleted (not touched yet) vim7",
+        \ ""], getline(1, '$'))
+
+  set compatible&vim
+  set visualbell&vim
+  set backspace&vim
+  close!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab