Add regression test for IMAP message deletion

Test times out while trying to delete messages. Message deletion jobs
don't complete in time because IMAP response parsing is broken in the
Rust core.

python/tests/test_account.py

@@ -1652,6 +1652,45 @@ class TestOnlineAccount:
         assert "Ephemeral timer: " not in system_message2.get_message_info()
         assert chat1.get_ephemeral_timer() == 0
 
+    @pytest.mark.xfail
+    def test_delete_multiple_messages(self, acfactory, lp):
+        ac1, ac2 = acfactory.get_two_online_accounts()
+        chat12 = acfactory.get_accepted_chat(ac1, ac2)
+
+        lp.sec("ac1: sending seven messages")
+        texts = ["first", "second", "third", "fourth", "fifth", "sixth", "seventh"]
+        for text in texts:
+            chat12.send_text(text)
+
+        lp.sec("ac2: waiting for all messages on the other side")
+        to_delete = []
+        for text in texts:
+            msg = ac2._evtracker.wait_next_incoming_message()
+            assert msg.text == text
+            if text != "third":
+                to_delete.append(msg)
+
+        lp.sec("ac2: deleting all messages except third")
+        assert len(to_delete) == len(texts) - 1
+        ac2.delete_messages(to_delete)
+        for msg in to_delete:
+            ac2._evtracker.get_matching("DC_EVENT_IMAP_MESSAGE_DELETED")
+
+        ac2._evtracker.get_info_contains("close/expunge succeeded")
+
+        lp.sec("imap2: test that only one message is left")
+        imap2 = ac2.direct_imap
+
+        # Flush unsolicited responses. IMAPClient has problems
+        # dealing with them: https://github.com/mjs/imapclient/issues/334
+        # When this NOOP was introduced, next FETCH returned empty
+        # result instead of a single message, even though IMAP server
+        # can only return more untagged responses than required, not
+        # less.
+        imap2.conn.noop()
+
+        assert len(imap2.get_all_messages()) == 1
+
 
 class TestGroupStressTests:
     def test_group_many_members_add_leave_remove(self, acfactory, lp):