tests: creating setup and tests for mdiarea

tests/test_mdiarea.py

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+import unittest
+import sys
+from PyQt5.QtWidgets import QMainWindow, QApplication
+
+from grum.mdi.mdiarea import MDIArea
+from grum.mainwin import MainWindow
+import mock
+
+class TestViewUnit(unittest.TestCase):
+    def setUp(self) -> None:
+        print("setup")
+        self.app = QApplication(sys.argv)
+        self.mw = MainWindow()
+        self.mw.show()
+
+    def tearDown(self) -> None:
+        print("teardown")
+        self.mw.rst.wait_for_stop()
+        self.app.quit()
+        print("app quit called")
+        del self.mw
+        del self.app
+
+    def test_on_cascade(self):
+        mdi = self.mw.mdi 
+
+        mdi.enable_subwindow_view = mock.MagicMock()
+        mdi.cascadeSubWindows = mock.MagicMock()
+        mdi.menu.checkboxes["Multiple windows"].setChecked(False)
+        assert mdi.menu.checkboxes["Multiple windows"].isChecked() == False
+
+        mdi.on_cascade()
+
+        assert mdi.menu.checkboxes["Multiple windows"].isChecked() == True
+        mdi.enable_subwindow_view.assert_called_once()
+        mdi.cascadeSubWindows.assert_called_once()