fix: differentiate click and drag for DeviceItem, adapt tests accordingly

This fixes the blocking "QDrag.exec_()" on Linux, indeed before the
drag'n'drop operation was started with a simple click and it was
waiting for drop forever. Now there are 2 different cases, click or
drag'n'drop - the drag'n'drop test actually moves the mouse and releases
the button.

bec_widgets/widgets/services/device_browser/device_item/device_item.py

@@ -5,7 +5,7 @@ from typing import TYPE_CHECKING
 from bec_lib.logger import bec_logger
 from qtpy.QtCore import QMimeData, Qt
 from qtpy.QtGui import QDrag
-from qtpy.QtWidgets import QHBoxLayout, QLabel, QWidget
+from qtpy.QtWidgets import QApplication, QHBoxLayout, QLabel, QWidget
 
 if TYPE_CHECKING:
     from qtpy.QtGui import QMouseEvent
@@ -16,6 +16,9 @@ logger = bec_logger.logger
 class DeviceItem(QWidget):
     def __init__(self, device: str) -> None:
         super().__init__()
+
+        self._drag_pos = None
+
         self.device = device
         layout = QHBoxLayout()
         layout.setContentsMargins(10, 2, 10, 2)
@@ -32,12 +35,21 @@ class DeviceItem(QWidget):
         )
 
     def mousePressEvent(self, event: QMouseEvent) -> None:
+        super().mousePressEvent(event)
         if event.button() == Qt.LeftButton:
-            drag = QDrag(self)
-            mime_data = QMimeData()
-            mime_data.setText(self.device)
-            drag.setMimeData(mime_data)
-            drag.exec_(Qt.MoveAction)
+            self._drag_pos = event.pos()
+
+    def mouseMoveEvent(self, event: QMouseEvent) -> None:
+        if not (event.buttons() and Qt.LeftButton):
+            return
+        if (event.pos() - self._drag_pos).manhattanLength() < QApplication.startDragDistance():
+            return
+
+        drag = QDrag(self)
+        mime_data = QMimeData()
+        mime_data.setText(self.device)
+        drag.setMimeData(mime_data)
+        drag.exec_(Qt.MoveAction)
 
     def mouseDoubleClickEvent(self, event: QMouseEvent) -> None:
         logger.debug("Double Clicked")

tests/unit_tests/test_device_browser.py

@@ -2,7 +2,7 @@ from typing import TYPE_CHECKING
 from unittest import mock
 
 import pytest
-from qtpy.QtCore import Qt
+from qtpy.QtCore import QPoint, Qt
 
 from bec_widgets.widgets.services.device_browser.device_browser import DeviceBrowser
 
@@ -55,10 +55,10 @@ def test_device_item_mouse_press_event(device_browser, qtbot):
     # Simulate a left mouse press event on the device item
     device_item: QListWidgetItem = device_browser.ui.device_list.itemAt(0, 0)
     widget: DeviceItem = device_browser.ui.device_list.itemWidget(device_item)
-    qtbot.mousePress(widget.label, Qt.MouseButton.LeftButton)
+    qtbot.mouseClick(widget.label, Qt.MouseButton.LeftButton)
 
 
-def test_device_item_mouse_press_event_creates_drag(device_browser, qtbot):
+def test_device_item_mouse_press_and_move_events_creates_drag(device_browser, qtbot):
     """
     Test that the mousePressEvent is triggered correctly and initiates a drag.
     """
@@ -67,7 +67,9 @@ def test_device_item_mouse_press_event_creates_drag(device_browser, qtbot):
     device_name = widget.device
     with mock.patch("qtpy.QtGui.QDrag.exec_") as mock_exec:
         with mock.patch("qtpy.QtGui.QDrag.setMimeData") as mock_set_mimedata:
-            qtbot.mousePress(widget.label, Qt.MouseButton.LeftButton)
+            qtbot.mousePress(widget.label, Qt.MouseButton.LeftButton, pos=QPoint(0, 0))
+            qtbot.mouseMove(widget, pos=QPoint(10, 10))
+            qtbot.mouseRelease(widget, Qt.MouseButton.LeftButton)
             mock_set_mimedata.assert_called_once()
             mock_exec.assert_called_once()
             assert mock_set_mimedata.call_args[0][0].text() == device_name