OWDistances: Do not show messages when data is removed

Orange/widgets/unsupervised/owdistances.py

@@ -99,11 +99,11 @@ def commit(self):
         self.send("Distances", self.compute_distances(metric, self.data))
 
     def compute_distances(self, metric, data):
+        self.clear_messages()
+
         if data is None:
             return
 
-        self.clear_messages()
-
         if issparse(data.X) and not metric.supports_sparse:
             self.Error.dense_metric_sparse_data()
             return

Orange/widgets/unsupervised/tests/test_owdistances.py

@@ -0,0 +1,42 @@
+# Test methods with long descriptive names can omit docstrings
+# pylint: disable=missing-docstring
+import numpy as np
+
+from Orange.data import Table
+from Orange.distance import MahalanobisDistance
+from Orange.widgets.unsupervised.owdistances import OWDistances, METRICS
+from Orange.widgets.tests.base import WidgetTest
+
+
+class TestOWDistances(WidgetTest):
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+        cls.iris = Table("iris")
+        cls.titanic = Table("titanic")
+
+    def setUp(self):
+        self.widget = self.create_widget(OWDistances)
+
+    def test_distance_combo(self):
+        """Check distances when the metric changes"""
+        self.assertEqual(self.widget.metrics_combo.count(), len(METRICS))
+        self.send_signal("Data", self.iris)
+        for i, metric in enumerate(METRICS):
+            if isinstance(metric, MahalanobisDistance):
+                metric.fit(self.iris)
+            self.widget.metrics_combo.activated.emit(i)
+            self.widget.metrics_combo.setCurrentIndex(i)
+            self.send_signal("Data", self.iris)
+            np.testing.assert_array_equal(
+                metric(self.iris), self.get_output("Distances"))
+
+    def test_error_message(self):
+        """Check if error message appears and then disappears when
+        data is removed from input"""
+        self.send_signal("Data", self.iris)
+        self.assertFalse(self.widget.Error.no_continuous_features.is_shown())
+        self.send_signal("Data", self.titanic)
+        self.assertTrue(self.widget.Error.no_continuous_features.is_shown())
+        self.send_signal("Data", None)
+        self.assertFalse(self.widget.Error.no_continuous_features.is_shown())