diff --git a/src/testdir/view_util.vim b/src/testdir/view_util.vim
index a0c1781..d9e740d 100644
--- a/src/testdir/view_util.vim
+++ b/src/testdir/view_util.vim
@@ -95,6 +95,18 @@
   return "\<Esc>[" .. key .. ';' .. mod .. 'u'
 endfunc
 
+" Return the kitty keyboard protocol encoding for a function key:
+" CSI {key}
+" CSS 1;{modifier} {key}
+func GetEscCodeFunckey(key, modifier)
+  if a:modifier == 0
+    return "\<Esc>[" .. a:key
+  endif
+
+  let mod = printf("%d", a:modifier)
+  return "\<Esc>[1;".. mod .. a:key
+endfunc
+
 " Return the kitty keyboard protocol encoding for "key" without a modifier.
 " Used for the Escape key.
 func GetEscCodeCSIuWithoutModifier(key)