Backported tests for issue #22406.
diff --git a/Lib/test/test_codecs.py b/Lib/test/test_codecs.py
index f2ec670..9f3b17a 100644
--- a/Lib/test/test_codecs.py
+++ b/Lib/test/test_codecs.py
@@ -2109,6 +2109,10 @@
         BomTest,
     )
 
+    def test_uu_invalid(self):
+        # Missing "begin" line
+        self.assertRaises(ValueError, codecs.decode, "", "uu-codec")
+
 
 if __name__ == "__main__":
     test_main()