test(dbus): Add support for testing driver reset notification

Introduce `FakeResetDriverWatchdog` to simulate driver reset triggers.
Update existing tests and add a new test, `test_notify_reset_driver`, to
verify reset notifications using the event signaling mechanism.

tests/dbus_middleware1/fake_devices.py

@@ -2,11 +2,13 @@
 # SPDX-FileCopyrightText: 2025 KUNBUS GmbH
 # SPDX-License-Identifier: GPL-2.0-or-later
 from ctypes import c_int
-from queue import Queue
+from queue import Empty, Queue
 from tempfile import NamedTemporaryFile
+from threading import Event, Thread
 from unittest import TestCase
 
 IOCTL_QUEUE = Queue()
+RESET_DRIVER_EVENT = Event()
 
 
 class FakePiControlDevice:
@@ -48,14 +50,67 @@ class FakePiControlDevice:
         return self._fh.write(buffer)
 
 
+class FakeResetDriverWatchdog(Thread):
+
+    def __init__(self, picontrol_device: str):
+        super().__init__()
+        self.daemon = True
+        self._calls = []
+        self._exit = False
+        self.not_implemented = True
+        self._triggered = False
+        self.start()
+
+    def run(self):
+        while not self._exit:
+            if RESET_DRIVER_EVENT.wait(0.1):
+                RESET_DRIVER_EVENT.clear()
+                self._triggered = True
+                for func in self._calls:
+                    func()
+
+    def register_call(self, function):
+        """Register a function, if watchdog triggers."""
+        if not callable(function):
+            raise ValueError("Function is not callable.")
+        if function not in self._calls:
+            self._calls.append(function)
+
+    def stop(self):
+        """Stop watchdog for reset_driver."""
+        self._exit = True
+
+    def unregister_call(self, function=None):
+        """Remove a function from the watchdog trigger."""
+        if function is None:
+            self._calls.clear()
+        elif function in self._calls:
+            self._calls.remove(function)
+
+    @property
+    def triggered(self):
+        """Will return True one time after watchdog was triggered."""
+        rc = self._triggered
+        self._triggered = False
+        return rc
+
+
 class PiControlDeviceMockup(TestCase):
 
     def setUp(self):
         super().setUp()
 
+        # Empty the queue
+        while True:
+            try:
+                IOCTL_QUEUE.get_nowait()
+            except Empty:
+                break
+
         # Replace classes with mockup classes
         import revpi_middleware.dbus_middleware1.process_image.interface_picontrol as test_helpers
         test_helpers.PiControlIoctl = FakePiControlDevice
+        test_helpers.ResetDriverWatchdog = FakeResetDriverWatchdog
 
         # Create a fake picontrol0 device
         self.picontrol = FakePiControlDevice(picontrol_device="/dev/fake_device_0")