Issue #23672: Allow Idle to edit and run files with astral chars in name.

Patch by Mohd Sanad Zaki Rizvi.

Lib/idlelib/idle_test/test_editor.py

@@ -0,0 +1,16 @@
+import unittest
+from tkinter import Tk, Text
+from idlelib.EditorWindow import EditorWindow
+from test.support import requires
+
+class Editor_func_test(unittest.TestCase):
+    def test_filename_to_unicode(self):
+        func = EditorWindow._filename_to_unicode
+        class dummy(): filesystemencoding = 'utf-8'
+        pairs = (('abc', 'abc'), ('a\U00011111c', 'a\ufffdc'),
+                 (b'abc', 'abc'), (b'a\xf0\x91\x84\x91c', 'a\ufffdc'))
+        for inp, out in pairs:
+            self.assertEqual(func(dummy, inp), out)
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2)