[tests] Close leftover server connections in the tcp_uart bridge and TCP client link tests (#20215)

Co-authored-by: J. Nick Koston <nick@koston.org>

tests/integration/test_socket_tcp_client_link.py

@@ -35,6 +35,7 @@ async def test_socket_tcp_client_link(
     link_down = asyncio.Event()
     second_link_up = asyncio.Event()
     link_up_count = 0
+    writers: list[asyncio.StreamWriter] = []
 
     def on_log_line(line: str) -> None:
         nonlocal link_up_count
@@ -48,6 +49,7 @@ async def test_socket_tcp_client_link(
     async def handle(
         reader: asyncio.StreamReader, writer: asyncio.StreamWriter
     ) -> None:
+        writers.append(writer)
         if not echo_done.is_set():
             writer.write(PAYLOAD)
             await writer.drain()
@@ -98,5 +100,9 @@ async def test_socket_tcp_client_link(
                 "Second session echo wrong; stale bytes from the first session?"
             )
     finally:
+        # On Python 3.12 wait_closed() waits for every connection the handlers
+        # left open; nothing else closes them once the device has exited.
+        for writer in writers:
+            writer.close()
         server.close()
         await server.wait_closed()

tests/integration/test_tcp_uart_bridge.py

@@ -41,12 +41,14 @@ async def test_tcp_uart_bridge(
     service_byte_ok = asyncio.Event()
     reconnect_echo_ok = asyncio.Event()
     sessions = 0
+    writers: list[asyncio.StreamWriter] = []
 
     async def handle(
         reader: asyncio.StreamReader, writer: asyncio.StreamWriter
     ) -> None:
         nonlocal sessions
         sessions += 1
+        writers.append(writer)
         if sessions == 1:
             writer.write(GREETING)
             await writer.drain()
@@ -98,5 +100,9 @@ async def test_tcp_uart_bridge(
                 reconnect_echo_ok, 15.0, "Bridge did not reconnect and echo again"
             )
     finally:
+        # On Python 3.12 wait_closed() waits for every connection the handlers
+        # left open; nothing else closes them once the device has exited.
+        for writer in writers:
+            writer.close()
         server.close()
         await server.wait_closed()