Merge pull request #3040 from ales-erjavec/fixes/test-owmosaic-join

[FIX] test_owmosaic: Cleanup/join threads on test tear down

Author: astaric

Orange/widgets/visualize/tests/test_owmosaic.py

@@ -114,6 +114,10 @@ def setUp(self):
         self.widget = self.create_widget(OWMosaicDisplay)
         self.vizrank = self.widget.vizrank
 
+    def tearDown(self):
+        self.widget.onDeleteWidget()
+        super().tearDown()
+
     def test_count(self):
         """MosaicVizrank correctly computes the number of combinations"""
         widget = self.widget