patch 9.0.0391: using separate delete() call instead of writefile() 'D' flag

Problem:    Using separate delete() call instead of writefile() 'D' flag.
Solution:   Use the writefile 'D' flag.
diff --git a/src/testdir/test_backup.vim b/src/testdir/test_backup.vim
index ee4b26f..68f2985 100644
--- a/src/testdir/test_backup.vim
+++ b/src/testdir/test_backup.vim
@@ -78,11 +78,11 @@
 " Test for using a non-existing directory as a backup directory
 func Test_non_existing_backupdir()
   set backupdir=./non_existing_dir backupskip=
-  call writefile(['line1'], 'Xbackupdir')
+  call writefile(['line1'], 'Xbackupdir', 'D')
   new Xbackupdir
   call assert_fails('write', 'E510:')
+
   set backupdir&vim backupskip&vim
-  call delete('Xbackupdir')
 endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/testdir/test_balloon.vim b/src/testdir/test_balloon.vim
index ed0c6c1..5e84f9e 100644
--- a/src/testdir/test_balloon.vim
+++ b/src/testdir/test_balloon.vim
@@ -29,7 +29,7 @@
       call feedkeys("\<MouseMove>\<Ignore>", "xt")
     endfunc
   [CODE]
-  call writefile(s:common_script + xtra_lines, 'XTest_beval')
+  call writefile(s:common_script + xtra_lines, 'XTest_beval', 'D')
 
   " Check that the balloon shows up after a mouse move
   let buf = RunVimInTerminal('-S XTest_beval', {'rows': 10, 'cols': 50})
@@ -45,7 +45,6 @@
 
   " clean up
   call StopVimInTerminal(buf)
-  call delete('XTest_beval')
 endfunc
 
 func Test_balloon_eval_term_visual()
@@ -54,7 +53,7 @@
   call writefile(s:common_script + [
 	\ 'call test_setmouse(3, 6)',
 	\ 'call feedkeys("3Gevfr\<MouseMove>\<Ignore>", "xt")',
-	\ ], 'XTest_beval_visual')
+	\ ], 'XTest_beval_visual', 'D')
 
   " Check that the balloon shows up after a mouse move
   let buf = RunVimInTerminal('-S XTest_beval_visual', {'rows': 10, 'cols': 50})
@@ -63,7 +62,6 @@
 
   " clean up
   call StopVimInTerminal(buf)
-  call delete('XTest_beval_visual')
 endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/testdir/test_breakindent.vim b/src/testdir/test_breakindent.vim
index 1c02294..f052fb7 100644
--- a/src/testdir/test_breakindent.vim
+++ b/src/testdir/test_breakindent.vim
@@ -902,14 +902,13 @@
       repeat('x', &columns - leftcol - 1)->setline(1)
       'second line'->setline(2)
   END
-  call writefile(lines, 'XscriptShowbreak')
+  call writefile(lines, 'XscriptShowbreak', 'D')
   let buf = RunVimInTerminal('-S XscriptShowbreak', #{rows: 6})
 
   call term_sendkeys(buf, "AX")
   call VerifyScreenDump(buf, 'Test_cursor_position_with_showbreak', {})
 
   call StopVimInTerminal(buf)
-  call delete('XscriptShowbreak')
 endfunc
 
 func Test_no_spurious_match()
diff --git a/src/testdir/test_buffer.vim b/src/testdir/test_buffer.vim
index 0d1741d..489926d 100644
--- a/src/testdir/test_buffer.vim
+++ b/src/testdir/test_buffer.vim
@@ -5,64 +5,60 @@
 " Test for the :bunload command with an offset
 func Test_bunload_with_offset()
   %bwipe!
-  call writefile(['B1'], 'b1')
-  call writefile(['B2'], 'b2')
-  call writefile(['B3'], 'b3')
-  call writefile(['B4'], 'b4')
+  call writefile(['B1'], 'Xb1', 'D')
+  call writefile(['B2'], 'Xb2', 'D')
+  call writefile(['B3'], 'Xb3', 'D')
+  call writefile(['B4'], 'Xb4', 'D')
 
   " Load four buffers. Unload the second and third buffers and then
   " execute .+3bunload to unload the last buffer.
-  edit b1
-  new b2
-  new b3
-  new b4
+  edit Xb1
+  new Xb2
+  new Xb3
+  new Xb4
 
-  bunload b2
-  bunload b3
-  exe bufwinnr('b1') . 'wincmd w'
+  bunload Xb2
+  bunload Xb3
+  exe bufwinnr('Xb1') . 'wincmd w'
   .+3bunload
-  call assert_equal(0, getbufinfo('b4')[0].loaded)
-  call assert_equal('b1',
+  call assert_equal(0, getbufinfo('Xb4')[0].loaded)
+  call assert_equal('Xb1',
         \ fnamemodify(getbufinfo({'bufloaded' : 1})[0].name, ':t'))
 
   " Load four buffers. Unload the third and fourth buffers. Execute .+3bunload
   " and check whether the second buffer is unloaded.
   ball
-  bunload b3
-  bunload b4
-  exe bufwinnr('b1') . 'wincmd w'
+  bunload Xb3
+  bunload Xb4
+  exe bufwinnr('Xb1') . 'wincmd w'
   .+3bunload
-  call assert_equal(0, getbufinfo('b2')[0].loaded)
-  call assert_equal('b1',
+  call assert_equal(0, getbufinfo('Xb2')[0].loaded)
+  call assert_equal('Xb1',
         \ fnamemodify(getbufinfo({'bufloaded' : 1})[0].name, ':t'))
 
   " Load four buffers. Unload the second and third buffers and from the last
   " buffer execute .-3bunload to unload the first buffer.
   ball
-  bunload b2
-  bunload b3
-  exe bufwinnr('b4') . 'wincmd w'
+  bunload Xb2
+  bunload Xb3
+  exe bufwinnr('Xb4') . 'wincmd w'
   .-3bunload
-  call assert_equal(0, getbufinfo('b1')[0].loaded)
-  call assert_equal('b4',
+  call assert_equal(0, getbufinfo('Xb1')[0].loaded)
+  call assert_equal('Xb4',
         \ fnamemodify(getbufinfo({'bufloaded' : 1})[0].name, ':t'))
 
   " Load four buffers. Unload the first and second buffers. Execute .-3bunload
   " from the last buffer and check whether the third buffer is unloaded.
   ball
-  bunload b1
-  bunload b2
-  exe bufwinnr('b4') . 'wincmd w'
+  bunload Xb1
+  bunload Xb2
+  exe bufwinnr('Xb4') . 'wincmd w'
   .-3bunload
-  call assert_equal(0, getbufinfo('b3')[0].loaded)
-  call assert_equal('b4',
+  call assert_equal(0, getbufinfo('Xb3')[0].loaded)
+  call assert_equal('Xb4',
         \ fnamemodify(getbufinfo({'bufloaded' : 1})[0].name, ':t'))
 
   %bwipe!
-  call delete('b1')
-  call delete('b2')
-  call delete('b3')
-  call delete('b4')
 
   call assert_fails('1,4bunload', 'E16:')
   call assert_fails(',100bunload', 'E16:')
@@ -76,9 +72,9 @@
   %bwipe!
   call assert_fails('buffer 1000', 'E86:')
 
-  call writefile(['foo1', 'foo2', 'foo3', 'foo4'], 'Xbrowse1')
-  call writefile(['bar1', 'bar2', 'bar3', 'bar4'], 'Xbrowse2')
-  call writefile(['baz1', 'baz2', 'baz3', 'baz4'], 'Xbrowse3')
+  call writefile(['foo1', 'foo2', 'foo3', 'foo4'], 'Xbrowse1', 'D')
+  call writefile(['bar1', 'bar2', 'bar3', 'bar4'], 'Xbrowse2', 'D')
+  call writefile(['baz1', 'baz2', 'baz3', 'baz4'], 'Xbrowse3', 'D')
   edit Xbrowse1
   let b1 = bufnr()
   edit Xbrowse2
@@ -127,9 +123,6 @@
 
   call assert_fails('sandbox bnext', 'E48:')
 
-  call delete('Xbrowse1')
-  call delete('Xbrowse2')
-  call delete('Xbrowse3')
   %bwipe!
 endfunc
 
@@ -200,13 +193,13 @@
 " Test for quitting the 'swapfile exists' dialog with the split buffer
 " command.
 func Test_buffer_sbuf_cleanup()
-  call writefile([], 'XsplitCleanup')
+  call writefile([], 'XsplitCleanup', 'D')
   " first open the file in a buffer
   new XsplitCleanup
   let bnr = bufnr()
   close
   " create the swap file
-  call writefile([], '.XsplitCleanup.swp')
+  call writefile([], '.XsplitCleanup.swp', 'D')
   " Remove the catch-all that runtest.vim adds
   au! SwapExists
   augroup BufTest
@@ -231,8 +224,6 @@
   call assert_equal(0, getbufinfo('XsplitCleanup')[0].loaded)
   set shortmess&
 
-  call delete('XsplitCleanup')
-  call delete('.XsplitCleanup.swp')
   augroup BufTest
     au!
   augroup END
@@ -325,8 +316,8 @@
 " Test for using CTRL-^ to edit the alternative file keeping the cursor
 " position with 'nostartofline'. Also test using the 'buf' command.
 func Test_buffer_edit_altfile()
-  call writefile(repeat(['one two'], 50), 'Xaltfile1')
-  call writefile(repeat(['five six'], 50), 'Xaltfile2')
+  call writefile(repeat(['one two'], 50), 'Xaltfile1', 'D')
+  call writefile(repeat(['five six'], 50), 'Xaltfile2', 'D')
   set nosol
   edit Xaltfile1
   call cursor(25, 5)
@@ -341,8 +332,6 @@
   buf Xaltfile2
   call assert_equal([0, 30, 4, 0], getpos('.'))
   set sol&
-  call delete('Xaltfile1')
-  call delete('Xaltfile2')
 endfunc
 
 " Test for running the :sball command with a maximum window count and a
@@ -494,7 +483,7 @@
   call assert_fails('%bw!', 'E342:')
 
   " test for :checktime loading the buffer
-  call writefile(['one'], 'XallocFail5')
+  call writefile(['one'], 'XallocFail5', 'D')
   if has('unix')
     edit XallocFail5
     " sleep for some time to make sure the timestamp is different
@@ -510,7 +499,6 @@
   " test for :vimgrep loading a dummy buffer
   call test_alloc_fail(GetAllocId('newbuf_bvars'), 0, 0)
   call assert_fails('vimgrep two XallocFail5', 'E342:')
-  call delete('XallocFail5')
 
   " test for quickfix command loading a buffer
   call test_alloc_fail(GetAllocId('newbuf_bvars'), 0, 0)
diff --git a/src/testdir/test_bufline.vim b/src/testdir/test_bufline.vim
index caf6aa7..f3502a3 100644
--- a/src/testdir/test_bufline.vim
+++ b/src/testdir/test_bufline.vim
@@ -81,11 +81,10 @@
   if cmd == ''
     return
   endif
-  call writefile(['call setline(1, "Hello")', 'silent w Xtest', 'q!'], 'Xscript')
+  call writefile(['call setline(1, "Hello")', 'silent w Xtest', 'q!'], 'Xscript', 'D')
   call system(cmd)
   call assert_equal(['Hello'], readfile('Xtest'))
 
-  call delete('Xscript')
   call delete('Xtest')
 endfunc
 
@@ -214,12 +213,11 @@
     call deletebufline(buf, 1, '$')
     call appendbufline(buf, '$', 'Hello Vim world...')
   END
-  call writefile(lines, 'XscriptMatchCommon')
+  call writefile(lines, 'XscriptMatchCommon', 'D')
   let buf = RunVimInTerminal('-S XscriptMatchCommon', #{rows: 10})
   call VerifyScreenDump(buf, 'Test_appendbufline_1', {})
 
   call StopVimInTerminal(buf)
-  call delete('XscriptMatchCommon')
 endfunc
 
 func Test_setbufline_select_mode()
diff --git a/src/version.c b/src/version.c
index 76ce3a1..2edbe83 100644
--- a/src/version.c
+++ b/src/version.c
@@ -704,6 +704,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    391,
+/**/
     390,
 /**/
     389,