virtual-device: Add test that open fails with a busy error if is still ongoing

The idea of the test was just checking what happens when we're opening a
device multiple times while a first request is still going.

However, it actually ends up also checking the previous commit change
because without it we'd stop the close iteration before the device is
actually closed and stop the open iteration before the device is
actually opened, leading to an infinite loop.

tests/virtual-device.py

@@ -730,6 +730,28 @@ class VirtualDeviceBusyDeviceOperations(VirtualDeviceBase):
             ctx.iteration(True)
         super().tearDown()
 
+    def test_open(self):
+        self.send_command('IGNORED_COMMAND')
+        self.send_sleep(100)
+
+        with GLibErrorMessage('libfprint-virtual_device',
+            GLib.LogLevelFlags.LEVEL_WARNING, 'Could not process command: *'):
+            while self.dev.is_open():
+                ctx.iteration(True)
+
+        self.assertFalse(self.dev.is_open())
+        self.dev.open()
+        with self.assertRaises(GLib.Error) as error:
+            self.dev.open_sync()
+        self.assertTrue(error.exception.matches(FPrint.DeviceError.quark(),
+                                                FPrint.DeviceError.BUSY))
+
+        self.assertFalse(self.dev.is_open())
+        while not self.dev.is_open():
+            ctx.iteration(True)
+
+        self.dev.close_sync()
+
     def test_close(self):
         with self.assertRaises(GLib.Error) as error:
             self.dev.close_sync()