patch 8.1.2148: no test for right click extending Visual area

Problem:    No test for right click extending Visual area.
Solution:   Add a test. (Dominique Pelle, closes #5018)

src/testdir/test_termcodes.vim

@@ -72,6 +72,14 @@ func MouseMiddleClick(row, col)
   endif
 endfunc
 
+func MouseRightClick(row, col)
+  if &ttymouse ==# 'dec'
+    call DecEscapeCode(6, 1, a:row, a:col)
+  else
+    call TerminalEscapeCode(2, a:row, a:col, 'M')
+  endif
+endfunc
+
 func MouseCtrlLeftClick(row, col)
   let ctrl = 0x10
   call TerminalEscapeCode(0 + ctrl, a:row, a:col, 'M')
@@ -101,7 +109,11 @@ func MouseMiddleRelease(row, col)
 endfunc
 
 func MouseRightRelease(row, col)
-  call TerminalEscapeCode(3, a:row, a:col, 'm')
+  if &ttymouse ==# 'dec'
+    call DecEscapeCode(7, 0, a:row, a:col)
+  else
+    call TerminalEscapeCode(3, a:row, a:col, 'm')
+  endif
 endfunc
 
 func MouseLeftDrag(row, col)
@@ -148,6 +160,79 @@ func Test_term_mouse_left_click()
   bwipe!
 endfunc
 
+func Test_xterm_mouse_right_click_extends_visual()
+  if has('mac')
+    throw "Skipped: test right click in visual mode does not work on macOs (why?)"
+  endif
+  let save_mouse = &mouse
+  let save_term = &term
+  let save_ttymouse = &ttymouse
+  call test_override('no_query_mouse', 1)
+  set mouse=a term=xterm
+
+  for visual_mode in ["v", "V", "\<C-V>"]
+    for ttymouse_val in s:ttymouse_values + s:ttymouse_dec
+      let msg = 'visual=' .. visual_mode .. ' ttymouse=' .. ttymouse_val
+      exe 'set ttymouse=' .. ttymouse_val
+
+      call setline(1, repeat([repeat('-', 7)], 7))
+      call MouseLeftClick(4, 4)
+      call MouseLeftRelease(4, 4)
+      exe  "norm! " .. visual_mode
+
+      " Right click extends top left of visual area.
+      call MouseRightClick(2, 2)
+      call MouseRightRelease(2, 2)
+
+      " Right click extends bottom bottom right of visual area.
+      call MouseRightClick(6, 6)
+      call MouseRightRelease(6, 6)
+      norm! r1gv
+
+      " Right click shrinks top left of visual area.
+      call MouseRightClick(3, 3)
+      call MouseRightRelease(3, 3)
+
+      " Right click shrinks bottom right of visual area.
+      call MouseRightClick(5, 5)
+      call MouseRightRelease(5, 5)
+      norm! r2
+
+      if visual_mode ==# 'v'
+        call assert_equal(['-------',
+              \            '-111111',
+              \            '1122222',
+              \            '2222222',
+              \            '2222211',
+              \            '111111-',
+              \            '-------'], getline(1, '$'), msg)
+      elseif visual_mode ==# 'V'
+        call assert_equal(['-------',
+              \            '1111111',
+              \            '2222222',
+              \            '2222222',
+              \            '2222222',
+              \            '1111111',
+              \            '-------'], getline(1, '$'), msg)
+      else
+        call assert_equal(['-------',
+              \            '-11111-',
+              \            '-12221-',
+              \            '-12221-',
+              \            '-12221-',
+              \            '-11111-',
+              \            '-------'], getline(1, '$'), msg)
+      endif
+    endfor
+  endfor
+
+  let &mouse = save_mouse
+  let &term = save_term
+  let &ttymouse = save_ttymouse
+  call test_override('no_query_mouse', 0)
+  bwipe!
+endfunc
+
 " Test that <C-LeftMouse> jumps to help tag and <C-RightMouse> jumps back.
 func Test_xterm_mouse_ctrl_click()
   let save_mouse = &mouse

src/version.c

@@ -753,6 +753,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2148,
 /**/
     2147,
 /**/