patch 9.1.0542: Vim9: confusing string() output for object functions

Problem:  Vim9: confusing string() output for object functions
Solution: improve the output for object functions (Ernie Rael)

fixes: #15129
closes: #15143

Signed-off-by: Ernie Rael <errael@raelity.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_vim9_class.vim b/src/testdir/test_vim9_class.vim
index 4f75a94..4654598 100644
--- a/src/testdir/test_vim9_class.vim
+++ b/src/testdir/test_vim9_class.vim
@@ -10466,6 +10466,20 @@
   call v9.CheckSourceSuccess(lines)
 endfunc
 
+" Test for using the string() builtin method with an object's method
+def Test_method_string()
+  var lines =<< trim END
+    vim9script
+    class A
+      def F()
+      enddef
+    endclass
+    assert_match('function(''<SNR>\d\+_A\.F'')', string(A.new().F))
+  END
+  v9.CheckScriptSuccess(lines)
+enddef
+
+
 " Test for using a class in the class definition
 def Test_Ref_Class_Within_Same_Class()
   var lines =<< trim END