fix: make background_fetch not wait on or trigger smtp connections

Also adds tests and docs to respective functions,
clarifying background fetching behaviour and the `ACCOUNTS_BACKGROUND_FETCH_DONE` event,
that came up in questions/discussions with UI devs lately.

deltachat-rpc-client/src/deltachat_rpc_client/const.py

@@ -70,6 +70,7 @@ class EventType(str, Enum):
     SELFAVATAR_CHANGED = "SelfavatarChanged"
     WEBXDC_STATUS_UPDATE = "WebxdcStatusUpdate"
     WEBXDC_INSTANCE_DELETED = "WebxdcInstanceDeleted"
+    ACCOUNTS_BACKGROUND_FETCH_DONE = "AccountsBackgroundFetchDone"
     CHATLIST_CHANGED = "ChatlistChanged"
     CHATLIST_ITEM_CHANGED = "ChatlistItemChanged"
     ACCOUNTS_CHANGED = "AccountsChanged"

deltachat-rpc-client/src/deltachat_rpc_client/deltachat.py

@@ -48,6 +48,13 @@ class DeltaChat:
         """Stop ongoing background fetch."""
         self.rpc.stop_background_fetch()
 
+    def wait_for_event(self, event_type=None) -> AttrDict:
+        """Wait until the next account manager event and return it."""
+        while True:
+            next_event = AttrDict(self.rpc.wait_for_event(0))
+            if event_type is None or next_event.kind == event_type:
+                return next_event
+
     def maybe_network(self) -> None:
         """Indicate that the network conditions might have changed."""
         self.rpc.maybe_network()

deltachat-rpc-client/tests/test_something.py

@@ -1354,6 +1354,22 @@ def test_background_fetch(acf, dc):
             break
 
 
+def test_background_fetch_does_not_wait_for_sending(dc, acf):
+    alice, bob = acf.get_online_accounts(2)
+    alice_chat_bob = alice.create_chat(bob)
+
+    alice.stop_io()
+    text = "x" * 200_000
+    for _ in range(50):
+        alice_chat_bob.send_text(text)
+    assert not dc.is_sending_finished()
+
+    alice.start_io()
+    dc.background_fetch(50)
+    dc.wait_for_event(EventType.ACCOUNTS_BACKGROUND_FETCH_DONE)
+    assert not dc.is_sending_finished()
+
+
 def test_message_exists(acf):
     ac1, ac2 = acf.get_online_accounts(2)
     chat = ac1.create_chat(ac2)