test(launch_window): add unit tests for LaunchWindow initialization and custom UI file launching

tests/unit_tests/test_launch_window.py

@@ -0,0 +1,48 @@
+# pylint: disable=missing-function-docstring, missing-module-docstring, unused-import
+
+import os
+
+import pytest
+from bec_lib.endpoints import MessageEndpoints
+
+import bec_widgets
+from bec_widgets.applications.launch_window import LaunchWindow
+from bec_widgets.widgets.containers.main_window.main_window import BECMainWindow, UILaunchWindow
+
+from .client_mocks import mocked_client
+
+base_path = os.path.dirname(bec_widgets.__file__)
+
+
+@pytest.fixture
+def bec_launch_window(qtbot, mocked_client):
+    widget = LaunchWindow(client=mocked_client)
+    qtbot.addWidget(widget)
+    qtbot.waitExposed(widget)
+    yield widget
+
+
+def test_launch_window_initialization(bec_launch_window):
+    assert isinstance(bec_launch_window, BECMainWindow)
+
+
+def test_launch_window_launch_ui_file(bec_launch_window):
+    # Mock the file dialog to return a specific UI file path
+    ui_file_path = os.path.join(
+        base_path, "widgets/control/device_control/positioner_box/positioner_box/positioner_box.ui"
+    )
+    bec_launch_window._open_custom_ui_file = lambda: ui_file_path
+
+    # Call the method to launch the custom UI file
+    res = bec_launch_window.launch("custom_ui_file", ui_file=ui_file_path)
+
+    assert isinstance(res, UILaunchWindow)
+
+    # Check if the custom UI file was launched correctly
+    assert res.object_name == "positioner_box"
+    assert res.windowTitle() == "BEC - positioner_box"
+
+    # We need to manually close the launched window as it is not registered with qtbot.
+    # In real usage, the GUIServer would handle this in the sigint handler in case of a ctrl-c initiated shutdown.
+    res.close()
+    res.deleteLater()