--- a/mercurial/transaction.py	Sat Jan 11 04:57:29 2020 +0100
+++ b/mercurial/transaction.py	Sat Jan 11 05:44:58 2020 +0100
@@ -456,6 +456,12 @@
         return self._anypending
 
     @active
+    def hasfinalize(self, category):
+        """check is a callback already exist for a category
+        """
+        return category in self._finalizecallback
+
+    @active
     def addfinalize(self, category, callback):
         """add a callback to be called when the transaction is closed