arsdk: prove one unnameable event does not take the link down

decode_event raises on an id triple the XML does not carry, and the XML
is missing at least FlatTrim, so this happens on a real aircraft. The
receive loop already counted and carried on; now something checks it.

tests/test_arsdk_session.py

@@ -397,3 +397,40 @@ def test_an_explicit_address_is_trusted_without_probing():
     assert found is not None
     assert (found.ip, found.via) == ("10.1.2.3", "given")
     assert found.address == ("10.1.2.3", 44444)
+
+
+# -- an event we cannot name ---------------------------------------------
+async def test_an_undecodable_event_is_counted_not_fatal(sim):
+    """`decode_event` raises on an id triple the XML does not have.
+
+    The XML is demonstrably incomplete, so this happens on a real aircraft.
+    One such event must not take the receive thread, and therefore the link,
+    down with it.
+    """
+    battery = _SPECS["common.CommonState.BatteryStateChanged"].ids
+
+    def decoder(payload):
+        ids = COMMAND_HEADER.unpack_from(payload)
+        if ids == battery:
+            raise ValueError(f"no command with ids {ids}")
+        return fake_decode(payload)
+
+    drone = DroneSession(
+        "127.0.0.1",
+        discovery_port=sim.discovery_port,
+        d2c_port=0,
+        timeouts=quick_timeouts(),
+        encoder=fake_encode,
+        decoder=decoder,
+    )
+    await drone.connect()
+    try:
+        assert await until(drone, "AttitudeChanged_roll") is not None
+        stats = drone.link_stats()
+        assert stats["undecodable_events"] > 0
+        assert "BatteryStateChanged_percent" not in drone.values()
+        # The rest of the stream kept arriving, and commands still work.
+        result = await drone.send(VIDEO_ENABLE, {"enable": 1}, confirm=False)
+        assert result["acked"] is True
+    finally:
+        await drone.disconnect()