Fix changing of alert_type on Alert pane (#1734)

* Fix changing of alert_type on Alert pane

* Fixed Markdown test

panel/pane/alert.py

@@ -21,7 +21,7 @@ class Alert(Markdown):
 
     priority = 0
 
-    _rename=dict(Markdown._rename, alert_type=None)
+    _rename = dict(Markdown._rename, alert_type=None)
 
     @classmethod
     def applies(cls, obj):

panel/pane/markup.py

@@ -269,7 +269,7 @@ class Markdown(DivPaneBase):
 
     _target_transforms = {'object': None}
 
-    _rerender_params = ['object', 'dedent', 'extensions']
+    _rerender_params = ['object', 'dedent', 'extensions', 'css_classes']
 
     @classmethod
     def applies(cls, obj):

panel/tests/pane/test_alert.py

@@ -16,13 +16,17 @@ def test_constructor():
 
 
 @pytest.mark.parametrize(["alert_type"], [(alert_type,) for alert_type in ALERT_TYPES])
-def test_alert_type_change(alert_type):
+def test_alert_type_change(alert_type, document, comm):
     """Test that an alert can change alert_type"""
     alert = Alert(text="This is some text")
 
+    model = alert.get_root(document, comm)
+
     alert.alert_type = alert_type
     assert set(alert.css_classes) == {"alert", f"alert-{alert_type}"}
+    assert set(model.css_classes) == {"alert", f"alert-{alert_type}", "markdown"}
 
+
 def test_existing_css_classes():
     """Test that an alert can change alert_type"""
     alert = Alert(text="This is some text", css_classes=["important"])

panel/tests/util.py

@@ -41,6 +41,8 @@
 
 py3_only = pytest.mark.skipif(sys.version_info.major < 3, reason="requires Python 3")
 
+from panel.pane.markup import Markdown
+
 
 def mpl_figure():
     import matplotlib.pyplot as plt
@@ -56,7 +58,10 @@ def check_layoutable_properties(layoutable, model):
     assert model.background == '#ffffff'
 
     layoutable.css_classes = ['custom_class']
-    assert model.css_classes == ['custom_class']
+    if isinstance(layoutable, Markdown):
+        assert model.css_classes == ['custom_class', 'markdown']
+    else:
+        assert model.css_classes == ['custom_class']
 
     layoutable.width = 500
     assert model.width == 500