patch 8.1.0025: no test for the undofile() function

Problem:    No test for the undofile() function.
Solution:   Add test. (Dominique Pelle, closes #2958)

src/testdir/test_undo.vim

@@ -85,7 +85,7 @@ endfunc
func FillBuffer()
  for i in range(1,13)
    put=i
    " Set 'undolevels' to split undo. 
    " Set 'undolevels' to split undo.
    exe "setg ul=" . &g:ul
  endfor
endfunc
@@ -193,19 +193,19 @@ func Test_undolist()
  new
  set ul=100

  let a=execute('undolist')
  let a = execute('undolist')
  call assert_equal("\nNothing to undo", a)

  " 1 leaf (2 changes).
  call feedkeys('achange1', 'xt')
  call feedkeys('achange2', 'xt')
  let a=execute('undolist')
  let a = execute('undolist')
  call assert_match("^\nnumber changes  when  *saved\n *2  *2 .*$", a)

  " 2 leaves.
  call feedkeys('u', 'xt')
  call feedkeys('achange3\<Esc>', 'xt')
  let a=execute('undolist')
  let a = execute('undolist')
  call assert_match("^\nnumber changes  when  *saved\n *2  *2  *.*\n *3  *2 .*$", a)
  close!
endfunc
@@ -339,7 +339,7 @@ endfunc
" Also test this in an empty buffer.
func Test_cmd_in_reg_undo()
  enew!
  let @a="Ox\<Esc>jAy\<Esc>kdd"
  let @a = "Ox\<Esc>jAy\<Esc>kdd"
  edit +/^$ test_undo.vim
  normal @au
  call assert_equal(0, &modified)
@@ -348,7 +348,7 @@ func Test_cmd_in_reg_undo()
  normal @au
  call assert_equal(0, &modified)
  only!
  let @a=''
  let @a = ''
endfunc

" This used to cause an illegal memory access
@@ -410,3 +410,35 @@ func Test_redo_empty_line()
  exe "norm."
  bwipe!
endfunc

funct Test_undofile()
  " Test undofile() without setting 'undodir'.
  if has('persistent_undo')
    call assert_equal(fnamemodify('.Xundofoo.un~', ':p'), undofile('Xundofoo'))
  else
    call assert_equal('', undofile('Xundofoo'))
  endif
  call assert_equal('', undofile(''))

  " Test undofile() with 'undodir' set to to an existing directory.
  call mkdir('Xundodir')
  set undodir=Xundodir
  let cwd = getcwd()
  if has('win32')
    " Replace windows drive such as C:... into C%...
    let cwd = substitute(cwd, '^\([A-Z]\):', '\1%', 'g')
  endif
  let cwd = substitute(cwd . '/Xundofoo', '/', '%', 'g')
  if has('persistent_undo')
    call assert_equal('Xundodir/' . cwd, undofile('Xundofoo'))
  else
    call assert_equal('', undofile('Xundofoo'))
  endif
  call assert_equal('', undofile(''))
  call delete('Xundodir', 'd')

  " Test undofile() with 'undodir' set to a non-existing directory.
  call assert_equal('', undofile('Xundofoo'))

  set undodir&
endfunc

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =

static int included_patches[] =
{   /* Add new patch number below this line */
/**/
    25,
/**/
    24,
/**/