Fix segfault in test_multidemo

qwt/tests/utils.py

@@ -237,11 +237,16 @@ def __init__(self, widget_name, parent=None):
         super(TestCentralWidget, self).__init__(parent)
         self.widget_name = widget_name
         self.plots = None
-        self.widget_of_interest = self.parent()
         self.setLayout(QW.QVBoxLayout())
         self.options = TestOptions(self)
         self.add_widget(self.options)
 
+    def get_widget_of_interest(self):
+        """Return widget of interest"""
+        if self.plots is not None and len(self.plots) == 1:
+            return self.plots[0]
+        return self.parent()
+
     def add_widget(self, widget):
         """Add new sub-widget"""
         self.layout().addWidget(widget)
@@ -257,8 +262,6 @@ def add_widget(self, widget):
                 plot_name, "Enable new flat style option", plot.setFlatStyle
             )
             widget.setChecked(plot.flatStyle())
-        if len(self.plots) == 1:
-            self.widget_of_interest = self.plots[0]
 
 
 def take_screenshot(widget):
@@ -297,7 +300,7 @@ def test_widget(widget_class, size=None, title=None, options=True):
         central_widget = TestCentralWidget(widget_name, parent=window)
         central_widget.add_widget(widget)
         window.setCentralWidget(central_widget)
-        widget_of_interest = central_widget.widget_of_interest
+        widget_of_interest = central_widget.get_widget_of_interest()
     else:
         widget_of_interest = window
     widget_of_interest.setObjectName(widget_name)