patch 8.1.1804: no test for display updating without a scroll region

Problem:    No test for display updating without a scroll region.
Solution:   Add a test.

src/testdir/check.vim

@@ -37,3 +37,20 @@ func CheckUnix()
     throw 'Skipped: only works on Unix'
   endif
 endfunc
+
+" Command to check that making screendumps is supported.
+" Caller must source screendump.vim
+command CheckScreendump call CheckScreendump()
+func CheckScreendump()
+  if !CanRunVimInTerminal()
+    throw 'Skipped: cannot make screendumps'
+  endif
+endfunc
+
+" Command to check that we can Run Vim in a terminal window
+command CheckRunVimInTerminal call CheckRunVimInTerminal()
+func CheckRunVimInTerminal()
+  if !CanRunVimInTerminal()
+    throw 'Skipped: cannot run Vim in a terminal window'
+  endif
+endfunc

src/testdir/dumps/Test_scroll_no_region_1.dump

@@ -0,0 +1,10 @@
+>1+0&#ffffff0| @73
+|2| @73
+|3| @73
+|4| @73
+|5| @73
+|6| @73
+|7| @73
+|8| @73
+|[+3&&|N|o| |N|a|m|e|]| |[|+|]| @43|1|,|1| @11|T|o|p
+| +0&&@74

src/testdir/dumps/Test_scroll_no_region_2.dump

@@ -0,0 +1,10 @@
+|1+0&#ffffff0| @73
+|2| @73
+>4| @73
+|5| @73
+|6| @73
+|7| @73
+|8| @73
+|9| @73
+|[+3&&|N|o| |N|a|m|e|]| |[|+|]| @43|3|,|1| @11|T|o|p
+| +0&&@74

src/testdir/dumps/Test_scroll_no_region_3.dump

@@ -0,0 +1,10 @@
+|1+0&#ffffff0| @73
+|2| @73
+|4| @73
+|5| @73
+>3| @73
+|6| @73
+|7| @73
+|8| @73
+|[+3&&|N|o| |N|a|m|e|]| |[|+|]| @43|5|,|1| @11|T|o|p
+| +0&&@74

src/testdir/test_diffmode.vim

@@ -1,6 +1,7 @@
 " Tests for diff mode
 source shared.vim
 source screendump.vim
+source check.vim
 
 func Test_diff_fold_sync()
   enew!
@@ -748,9 +749,9 @@ func VerifyInternal(buf, dumpfile, extra)
 endfunc
 
 func Test_diff_screen()
-  if !CanRunVimInTerminal() || !has('menu')
-    throw 'Skipped: cannot make screendumps and/or menu feature missing'
-  endif
+  CheckScreendump
+  CheckFeature menu
+
   " clean up already existing swap files, just in case
   call delete('.Xfile1.swp')
   call delete('.Xfile2.swp')
@@ -880,9 +881,7 @@ func Test_diff_screen()
 endfunc
 
 func Test_diff_with_cursorline()
-  if !CanRunVimInTerminal()
-    throw 'Skipped: cannot run Vim in a terminal window'
-  endif
+  CheckScreendump
 
   call writefile([
 	\ 'hi CursorLine ctermbg=red ctermfg=white',
@@ -907,12 +906,8 @@ func Test_diff_with_cursorline()
 endfunc
 
 func Test_diff_of_diff()
-  if !CanRunVimInTerminal()
-    throw 'Skipped: cannot run Vim in a terminal window'
-  endif
-  if !has("rightleft")
-    throw 'Skipped: rightleft not supported'
-  endif
+  CheckScreendump
+  CheckFeature rightleft
 
   call writefile([
 	\ 'call setline(1, ["aa","bb","cc","@@ -3,2 +5,7 @@","dd","ee","ff"])',

src/testdir/test_display.vim

@@ -4,11 +4,12 @@ if !has('gui_running') && has('unix')
 endif
 
 source view_util.vim
+source check.vim
+source screendump.vim
 
 func Test_display_foldcolumn()
-  if !has("folding")
-    return
-  endif
+  CheckFeature folding
+
   new
   vnew
   vert resize 25
@@ -24,10 +25,10 @@ func Test_display_foldcolumn()
 
   call cursor(2, 1)
   norm! zt
-  let lines=ScreenLines([1,2], winwidth(0))
+  let lines = ScreenLines([1,2], winwidth(0))
   call assert_equal(expect, lines)
   set fdc=2
-  let lines=ScreenLines([1,2], winwidth(0))
+  let lines = ScreenLines([1,2], winwidth(0))
   let expect = [
         \ "  e more noise blah blah<",
         \ "  82> more stuff here    "
@@ -39,9 +40,8 @@ func Test_display_foldcolumn()
 endfunc
 
 func Test_display_foldtext_mbyte()
-  if !has("folding")
-    return
-  endif
+  CheckFeature folding
+
   call NewWindow(10, 40)
   call append(0, range(1,20))
   exe "set foldmethod=manual foldtext=foldtext() fillchars=fold:\u2500,vert:\u2502 fdc=2"
@@ -67,3 +67,28 @@ func Test_display_foldtext_mbyte()
   set foldtext& fillchars& foldmethod& fdc&
   bw!
 endfunc
+
+" check that win_ins_lines() and win_del_lines() work when t_cs is empty.
+func Test_scroll_without_region()
+  CheckScreendump
+
+  let lines =<< trim END
+    call setline(1, range(1, 20))
+    set t_cs=
+    set laststatus=2
+  END
+  call writefile(lines, 'Xtestscroll')
+  let buf = RunVimInTerminal('-S Xtestscroll', #{rows: 10})
+
+  call VerifyScreenDump(buf, 'Test_scroll_no_region_1', {})
+
+  call term_sendkeys(buf, ":3delete\<cr>")
+  call VerifyScreenDump(buf, 'Test_scroll_no_region_2', {})
+
+  call term_sendkeys(buf, ":4put\<cr>")
+  call VerifyScreenDump(buf, 'Test_scroll_no_region_3', {})
+
+  " clean up
+  call StopVimInTerminal(buf)
+  call delete('Xtestscroll')
+endfunc

src/version.c

@@ -773,6 +773,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1804,
 /**/
     1803,
 /**/