Test recovery from lost member removal message

This was fixed in d98d1857a4 but not
tested.

Revert d98d1857a4 to check that the test
is working.

src/chat.rs

@@ -3598,6 +3598,49 @@ mod tests {
         Ok(())
     }
 
+    /// Test that group updates are robust to lost messages and eventual out of order arrival.
+    #[async_std::test]
+    async fn test_modify_chat_lost() -> Result<()> {
+        let alice = TestContext::new_alice().await;
+
+        let bob_id = Contact::create(&alice, "", "bob@example.net").await?;
+        let claire_id = Contact::create(&alice, "", "claire@foo.de").await?;
+        let daisy_id = Contact::create(&alice, "", "daisy@bar.de").await?;
+
+        let alice_chat_id = create_group_chat(&alice, ProtectionStatus::Unprotected, "foo").await?;
+        add_contact_to_chat(&alice, alice_chat_id, bob_id).await?;
+        add_contact_to_chat(&alice, alice_chat_id, claire_id).await?;
+        add_contact_to_chat(&alice, alice_chat_id, daisy_id).await?;
+
+        send_text_msg(&alice, alice_chat_id, "populate".to_string()).await?;
+        let add = alice.pop_sent_msg().await;
+        async_std::task::sleep(std::time::Duration::from_millis(1100)).await;
+
+        remove_contact_from_chat(&alice, alice_chat_id, claire_id).await?;
+        let remove1 = alice.pop_sent_msg().await;
+        async_std::task::sleep(std::time::Duration::from_millis(1100)).await;
+
+        remove_contact_from_chat(&alice, alice_chat_id, daisy_id).await?;
+        let remove2 = alice.pop_sent_msg().await;
+
+        let bob = TestContext::new_bob().await;
+
+        bob.recv_msg(&add).await;
+        let bob_chat_id = bob.get_last_msg().await.chat_id;
+        assert_eq!(get_chat_contacts(&bob, bob_chat_id).await?.len(), 4);
+
+        // First removal message is lost.
+        // Nevertheless, two members are removed.
+        bob.recv_msg(&remove2).await;
+        assert_eq!(get_chat_contacts(&bob, bob_chat_id).await?.len(), 2);
+
+        // Eventually, first removal message arrives.
+        // This has no effect.
+        bob.recv_msg(&remove1).await;
+        assert_eq!(get_chat_contacts(&bob, bob_chat_id).await?.len(), 2);
+        Ok(())
+    }
+
     #[async_std::test]
     async fn test_add_remove_contact_for_single() {
         let ctx = TestContext::new_alice().await;