patch 8.2.3108: test for remote_foreground() fails

Problem:    Test for remote_foreground() fails. (Elimar Riesebieter)
Solution:   Check that $DISPLAY is set. (Christian Brabandt)

src/testdir/check.vim

@@ -136,6 +136,14 @@ func CheckCanRunGui()
   endif
 endfunc
 
+" Command to Check for an environment variable
+command -nargs=1 CheckEnv call CheckEnv(<f-args>)
+func CheckEnv(name)
+  if empty('$' .. a:name)
+    throw 'Skipped: Environment variable ' .. a:name .. ' is not set'
+  endif
+endfunc
+
 " Command to check that we are using the GUI
 command CheckGui call CheckGui()
 func CheckGui()

src/testdir/test_clientserver.vim

@@ -13,9 +13,7 @@ source shared.vim
 
 func Check_X11_Connection()
   if has('x11')
-    if empty($DISPLAY)
-      throw 'Skipped: $DISPLAY is not set'
-    endif
+    CheckEnv DISPLAY
     try
       call remote_send('xxx', '')
     catch

src/testdir/test_vim9_builtin.vim

@@ -1415,6 +1415,8 @@ def Test_remote_foreground()
   CheckFeature clientserver
   # remote_foreground() doesn't fail on MS-Windows
   CheckNotMSWindows
+  CheckEnv DISPLAY
+
   CheckDefFailure(['remote_foreground(10)'], 'E1013: Argument 1: type mismatch, expected string but got number')
   assert_fails('remote_foreground("NonExistingServer")', 'E241:')
 enddef

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3108,
 /**/
     3107,
 /**/