OWDataSampler: Do not show messages when data is removed

Orange/widgets/data/owdatasampler.py

@@ -175,6 +175,7 @@ def set_data(self, dataset):
             self.dataInfoLabel.setText('No data on input.')
             self.outputInfoLabel.setText('')
             self.indices = None
+            self.clear_messages()
         self.commit()
 
     def commit(self):

Orange/widgets/data/tests/test_owdatasampler.py

@@ -0,0 +1,27 @@
+# Test methods with long descriptive names can omit docstrings
+# pylint: disable=missing-docstring
+from Orange.data import Table
+from Orange.widgets.data.owdatasampler import OWDataSampler
+from Orange.widgets.tests.base import WidgetTest
+
+
+class TestOWDataSampler(WidgetTest):
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+        cls.iris = Table("iris")
+
+    def setUp(self):
+        self.widget = self.create_widget(OWDataSampler)
+
+    def test_error_message(self):
+        """ Check if error message appears and then disappears when
+        data is removed from input"""
+        self.widget.controlledAttributes["sampling_type"][0].control.buttons[
+            2].click()
+        self.send_signal("Data", self.iris)
+        self.assertFalse(self.widget.Error.too_many_folds.is_shown())
+        self.send_signal("Data", self.iris[:5])
+        self.assertTrue(self.widget.Error.too_many_folds.is_shown())
+        self.send_signal("Data", None)
+        self.assertFalse(self.widget.Error.too_many_folds.is_shown())