Fail with descriptive errors when coordinator is disconnected

tests/api/test_request.py

@@ -318,3 +318,13 @@ async def test_handling_unknown_bad_command_parsing(connected_znp):
 
     with pytest.raises(ValueError):
         znp.frame_received(bad_frame)
+
+
+async def test_send_failure_when_disconnected(connected_znp):
+    znp, _ = connected_znp
+    znp._uart = None
+
+    with pytest.raises(RuntimeError) as e:
+        await znp.request(c.SYS.Ping.Req())
+
+    assert "Coordinator is disconnected" in str(e.value)

tests/application/test_requests.py

@@ -1009,3 +1009,29 @@ async def test_send_packet_failure(device, make_application, mocker):
     assert excinfo.value.status == t.Status.MAC_NO_ACK
 
     await app.shutdown()
+
+
+@pytest.mark.parametrize("device", FORMED_DEVICES)
+async def test_send_packet_failure_disconnected(device, make_application, mocker):
+    app, znp_server = await make_application(server_cls=device)
+    await app.startup(auto_form=False)
+
+    app._znp = None
+
+    packet = zigpy_t.ZigbeePacket(
+        src=zigpy_t.AddrModeAddress(addr_mode=zigpy_t.AddrMode.NWK, address=0x0000),
+        src_ep=0x9A,
+        dst=zigpy_t.AddrModeAddress(addr_mode=zigpy_t.AddrMode.NWK, address=0xEEFF),
+        dst_ep=0xBC,
+        tsn=0xDE,
+        profile_id=0x1234,
+        cluster_id=0x0006,
+        data=zigpy_t.SerializableBytes(b"test data"),
+    )
+
+    with pytest.raises(zigpy.exceptions.DeliveryError) as excinfo:
+        await app.send_packet(packet)
+
+    assert "Coordinator is disconnected" in str(excinfo.value)
+
+    await app.shutdown()

zigpy_znp/api.py

@@ -969,6 +969,9 @@ async def request(
 
         frame = request.to_frame(align=self.nvram.align_structs)
 
+        if self._uart is None:
+            raise RuntimeError("Coordinator is disconnected, cannot send request")
+
         # We should only be sending one SREQ at a time, according to the spec
         async with self._sync_request_lock:
             LOGGER.debug("Sending request: %s", request)

zigpy_znp/zigbee/application.py

@@ -839,6 +839,9 @@ async def _send_request_raw(
                 Data=data,
             )
 
+        if self._znp is None:
+            raise DeliveryError("Coordinator is disconnected, cannot send request")
+
         # Z-Stack requires special treatment when sending ZDO requests
         if dst_ep == ZDO_ENDPOINT:
             # XXX: Joins *must* be sent via a ZDO command, even if they are directly