Add python test for gossip optimization

python/tests/test_account.py

@@ -1221,6 +1221,40 @@ class TestOnlineAccount:
         assert not msg.is_encrypted()
         ac1._evtracker.get_matching("DC_EVENT_SMTP_MESSAGE_SENT")
 
+    def test_gossip_optimization(self, acfactory, lp):
+        """Test that gossip timestamp is updated when someone else sends gossip,
+        so we don't have to send gossip ourselves.
+        """
+        ac1, ac2, ac3 = acfactory.get_many_online_accounts(3)
+
+        acfactory.introduce_each_other([ac1, ac2])
+        acfactory.introduce_each_other([ac2, ac3])
+
+        lp.sec("ac1 creates a group chat with ac2")
+        group_chat = ac1.create_group_chat("hello")
+        group_chat.add_contact(ac2)
+        msg = group_chat.send_text("hi")
+
+        # No Autocrypt gossip was sent yet.
+        gossiped_timestamp = msg.chat.get_summary()["gossiped_timestamp"]
+        assert gossiped_timestamp == 0
+
+        msg = ac2._evtracker.wait_next_incoming_message()
+        assert msg.is_encrypted()
+        assert msg.text == "hi"
+
+        lp.sec("ac2 adds ac3 to the group")
+        msg.chat.add_contact(ac3)
+
+        lp.sec("ac1 receives message from ac2 and updates gossip timestamp")
+        msg = ac1._evtracker.wait_next_incoming_message()
+        assert msg.is_encrypted()
+
+        # ac1 has updated the gossip timestamp even though no gossip was sent by ac1.
+        # ac1 does not need to send gossip because ac2 already did it.
+        gossiped_timestamp = msg.chat.get_summary()["gossiped_timestamp"]
+        assert gossiped_timestamp == int(msg.time_sent.timestamp())
+
     def test_gossip_encryption_preference(self, acfactory, lp):
         """Test that encryption preference of group members is gossiped to new members.
         This is a Delta Chat extension to Autocrypt 1.1.0, which Autocrypt-Gossip headers