Add a test for a LayerArtist responding to updated components

glue/viewers/common/tests/test_viewer.py

@@ -3,6 +3,7 @@
 from glue.core import Data
 from glue.viewers.common.viewer import Viewer
 from glue.viewers.common.layer_artist import LayerArtist
+from glue.core.message import NumericalDataChangedMessage
 
 
 def test_custom_layer_artist_maker():
@@ -45,3 +46,60 @@ def custom_maker(viewer, data):
     viewer.add_data(data2)
     assert len(viewer.layers) == 2
     assert type(viewer.layers[1]) is CustomLayerArtist
+
+
+def test_viewer_update_data():
+    """
+    Test that we can have a LayerArtist that can respond
+    to a NumericalDataChangedMessage.
+    """
+
+    class CustomUpdateLayerArtist(LayerArtist):
+
+        def update_component_limits(self, components_changed):
+            self.called_component_limits = True
+            self.num_components_changed = len(components_changed)
+
+    class CustomApplication(Application):
+        def add_widget(self, *args, **kwargs):
+            pass
+
+    @layer_artist_maker('custom_maker_for_update')
+    def custom_maker_for_update(viewer, data):
+        if hasattr(data, 'custom_for_update'):
+            return CustomUpdateLayerArtist(viewer.state, layer=data)
+        if hasattr(data.data, 'custom_for_update'):
+            return CustomUpdateLayerArtist(viewer.state, layer=data)
+
+    app = CustomApplication()
+
+    data1 = Data(x=[1, 2, 3], label='test1')
+    data1.custom_for_update = True
+
+    app.data_collection.append(data1)
+
+    viewer = app.new_data_viewer(Viewer)
+
+    assert len(viewer.layers) == 0
+
+    # NOTE: Check exact type, not using isinstance
+    viewer.add_data(data1)
+    assert len(viewer.layers) == 1
+    assert type(viewer.layers[0]) is CustomUpdateLayerArtist
+
+    msg = NumericalDataChangedMessage(data1, components_changed=[data1.id['x']])
+
+    viewer._update_data(msg)
+    assert viewer.layers[0].called_component_limits
+    assert viewer.layers[0].num_components_changed == 1
+
+    subset = data1.new_subset()
+    subset.subset_state = data1.id['x'] > 2
+
+    assert len(viewer.layers) == 2
+    assert type(viewer.layers[1]) is CustomUpdateLayerArtist
+
+    msg = NumericalDataChangedMessage(data1, components_changed=[data1.id['x']])
+    viewer._update_data(msg)
+    assert viewer.layers[1].called_component_limits
+    assert viewer.layers[1].num_components_changed == 1