diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index b4d11ac..8a56110 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -2057,6 +2057,7 @@ func Test_cmdlineclear_tabenter()
   CheckScreendump
 
   let lines =<< trim [SCRIPT]
+    set mouse=a
     call setline(1, range(30))
   [SCRIPT]
 
diff --git a/src/testdir/test_diffmode.vim b/src/testdir/test_diffmode.vim
index 7e93ea3..64ada23 100644
--- a/src/testdir/test_diffmode.vim
+++ b/src/testdir/test_diffmode.vim
@@ -2213,6 +2214,7 @@ func Test_diff_overlapped_diff_blocks_will_be_merged()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     func DiffExprStub()
       let txt_in = readfile(v:fname_in)
       let txt_new = readfile(v:fname_new)
@@ -2228,7 +2230,7 @@ func Test_diff_overlapped_diff_blocks_will_be_merged()
   call writefile(lines, 'XdiffSetup', 'D')
 
   call WriteDiffFiles(0, [], [])
-  let buf = RunVimInTerminal('-d -S XdiffSetup Xdifile1 Xdifile2', {})
+  let buf = RunVimInTerminal('-d -S XdiffSetup Xdifile1 Xdifile2 -c ":set mouse=a"', {})
   call term_sendkeys(buf, ":set autoread\<CR>\<c-w>w:set autoread\<CR>\<c-w>w")
 
   call WriteDiffFiles(buf, ["a", "b"], ["x", "x"])
@@ -2470,7 +2472,7 @@ func Test_diff_inline()
   CheckScreendump
 
   call WriteDiffFiles(0, [], [])
-  let buf = RunVimInTerminal('-d Xdifile1 Xdifile2', {})
+  let buf = RunVimInTerminal('-d Xdifile1 Xdifile2 -c ":set mouse=a"', {})
   call term_sendkeys(buf, ":set autoread\<CR>\<c-w>w:set autoread\<CR>\<c-w>w")
 
   call WriteDiffFiles(buf, ["abcdef ghi jk n", "x", "y"], ["aBcef gHi lm n", "y", "z"])
@@ -2899,7 +2901,7 @@ func Test_linematch_diff_iwhite()
   call delete('.Xdifile2.swp')
   call WriteDiffFiles(0, [], [])
   let buf = RunVimInTerminal('-d Xdifile1 Xdifile2', {})
-  call term_sendkeys(buf, ":set autoread\<CR>\<c-w>w:set autoread\<CR>\<c-w>w")
+  call term_sendkeys(buf, ":set autoread\<CR>:set mouse=a\<CR>\<c-w>w:set autoread\<CR>:set mouse=a\<CR>\<c-w>w")
 
   " setup a diff with 2 files and set linematch:30, with ignore white
   call term_sendkeys(buf, ":set diffopt=internal,filler,linematch:30\<CR>")
@@ -2925,7 +2927,7 @@ func Test_linematch_diff_grouping()
   call delete('.Xdifile1.swp')
   call delete('.Xdifile2.swp')
   call WriteDiffFiles(0, [], [])
-  let buf = RunVimInTerminal('-d Xdifile1 Xdifile2', {})
+  let buf = RunVimInTerminal('-d Xdifile1 Xdifile2 -c ":set mouse=a"', {})
   call term_sendkeys(buf, ":set autoread\<CR>\<c-w>w:set autoread\<CR>\<c-w>w")
 
   " a diff that would result in multiple groups before grouping optimization
diff --git a/src/testdir/test_ins_complete.vim b/src/testdir/test_ins_complete.vim
index 37553e6..6e9103c 100644
--- a/src/testdir/test_ins_complete.vim
+++ b/src/testdir/test_ins_complete.vim
@@ -883,6 +883,7 @@ func Test_pum_with_folds_two_tabs()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     set fdm=marker
     call setline(1, ['" x {{{1', '" a some text'])
     call setline(3, range(&lines)->map({_, val -> '" a' .. val}))
@@ -6045,6 +6046,7 @@ endfunc
 func Test_fuzzy_select_item_when_acl()
   CheckScreendump
   let lines =<< trim [SCRIPT]
+    set mouse=a
     call setline(1, ["v", "vi", "vim"])
     set autocomplete completeopt=menuone,noinsert,fuzzy autocompletedelay=300
   [SCRIPT]
diff --git a/src/testdir/test_messages.vim b/src/testdir/test_messages.vim
index 0942fe2..baa5e4f 100644
--- a/src/testdir/test_messages.vim
+++ b/src/testdir/test_messages.vim
@@ -617,6 +617,7 @@ func Test_echowindow()
   CheckScreendump
 
   let lines =<< trim END
+      set mouse=a
       call setline(1, 'some text')
       func ShowMessage(arg)
         echowindow a:arg
diff --git a/src/testdir/test_plugin_termdebug.vim b/src/testdir/test_plugin_termdebug.vim
index 1f6fd36..5decd00 100644
--- a/src/testdir/test_plugin_termdebug.vim
+++ b/src/testdir/test_plugin_termdebug.vim
@@ -333,6 +333,7 @@ func Test_termdebug_evaluate_in_popup()
   call system($'{g:GCC} -g -o {bin_name} {src_name}')
 
   let lines =<< trim END
+    set mouse=a
     edit XTD_evaluate_in_popup.c
     packadd termdebug
     let g:termdebug_config = {}
diff --git a/src/testdir/test_popup.vim b/src/testdir/test_popup.vim
index 9086ebb..5ccfcbb 100644
--- a/src/testdir/test_popup.vim
+++ b/src/testdir/test_popup.vim
@@ -2205,6 +2205,7 @@ func Test_pum_clear_when_switch_tab_or_win()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     inoremap <F4> <Cmd>wincmd w<CR>
     inoremap <F5> <Cmd>tabnext<CR>
   END
diff --git a/src/testdir/test_popupwin.vim b/src/testdir/test_popupwin.vim
index 0348169..7bc1446 100644
--- a/src/testdir/test_popupwin.vim
+++ b/src/testdir/test_popupwin.vim
@@ -8,6 +8,7 @@ func Test_simple_popup()
   CheckScreendump
 
   let lines =<< trim END
+        set mouse=a
 	call setline(1, range(1, 100))
 	hi PopupColor1 ctermbg=lightblue
 	hi PopupColor2 ctermbg=lightcyan
@@ -3531,6 +3532,7 @@ endfunc
 
 func Get_popupmenu_lines()
   let lines =<< trim END
+      set mouse=a
       set completeopt+=preview,popup
       set completefunc=CompleteFuncDict
       hi InfoPopup ctermbg=yellow
@@ -3792,6 +3794,7 @@ endfunc
 func Test_popupmenu_info_align_item()
   CheckScreendump
   let lines =<< trim END
+    set mouse=a
     func Omni_test(findstart, base)
         if a:findstart
             return col(".")
diff --git a/src/testdir/test_startup.vim b/src/testdir/test_startup.vim
index 6693a76..3275324 100644
--- a/src/testdir/test_startup.vim
+++ b/src/testdir/test_startup.vim
@@ -930,7 +930,7 @@ func Test_start_with_tabs()
   CheckScreendump
   CheckRunVimInTerminal
 
-  let buf = RunVimInTerminal('-p a b c', {})
+  let buf = RunVimInTerminal('-c ":set mouse=a" -p a b c', {})
   call VerifyScreenDump(buf, 'Test_start_with_tabs', {})
 
   " clean up
diff --git a/src/testdir/test_tabpage.vim b/src/testdir/test_tabpage.vim
index 05c5669..436423f 100644
--- a/src/testdir/test_tabpage.vim
+++ b/src/testdir/test_tabpage.vim
@@ -690,6 +690,7 @@ func Test_tabpage_cmdheight()
   CheckScreendump
   CheckRunVimInTerminal
   call writefile([
+        \ 'set mouse=a',
         \ 'set laststatus=2',
         \ 'set cmdheight=2',
         \ 'tabnew',
diff --git a/src/testdir/test_tabpanel.vim b/src/testdir/test_tabpanel.vim
index 4959693..9306be0 100644
--- a/src/testdir/test_tabpanel.vim
+++ b/src/testdir/test_tabpanel.vim
@@ -13,6 +13,7 @@ function Test_tabpanel_showtabpanel_eq_0()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     set showtabpanel=2
     set noruler
     call setbufline(bufnr(), 1, ['aaa','bbb','ccc','ddd'])
@@ -40,6 +41,7 @@ function Test_tabpanel_showtabpanel_eq_1()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     set showtabpanel=1
     set noruler
   END
@@ -491,6 +493,7 @@ function Test_tabpanel_tabline_and_tabpanel()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     set showtabpanel=2
     set tabpanelopt=columns:10,vert
     set fillchars=tpl_vert:│
@@ -513,6 +516,7 @@ function Test_tabpanel_dont_overflow_into_tabpanel()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     set showtabpanel=2
     set tabpanelopt=columns:10
     set showtabline=2
@@ -643,6 +647,7 @@ function Test_tabpanel_eval_tabpanel_with_linebreaks()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     function Expr()
       return "top\n$%=[%f]%=$\nbottom"
     endfunction
@@ -670,6 +675,7 @@ function Test_tabpanel_tabonly()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     tabnew
     set showtabpanel=1
     norm 100oasdf
@@ -689,6 +695,7 @@ function Test_tabpanel_equalalways()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     tabnew
     set showtabpanel=1
     set tabpanelopt=columns:20
@@ -714,6 +721,7 @@ function Test_tabpanel_quitall()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     tabnew
     set showtabpanel=1
     set laststatus=2
@@ -733,6 +741,7 @@ function Test_tabpanel_ruler()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     tabnew
     set statusline& laststatus=0
     set rulerformat& ruler
@@ -770,6 +779,7 @@ function Test_tabpanel_with_msg_scrolled()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     set showtabpanel=2
     set noruler
     tabnew
@@ -791,6 +801,7 @@ function Test_tabpanel_with_cmdline_pum()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     set showtabpanel=2
     set noruler
     tabnew aaa
@@ -818,6 +829,7 @@ function Test_tabpanel_with_cmdline_no_pum()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     set showtabpanel=2
     set noruler
     tabnew aaa
diff --git a/src/testdir/test_window_cmd.vim b/src/testdir/test_window_cmd.vim
index 02e6fcb..746a905 100644
--- a/src/testdir/test_window_cmd.vim
+++ b/src/testdir/test_window_cmd.vim
@@ -2360,6 +2360,7 @@ func Test_resize_from_another_tabpage()
   CheckScreendump
 
   let lines =<< trim END
+    set mouse=a
     set laststatus=2
     vnew
     let w = win_getid()