feat(listview): skeleton loading states for table and card collections (#10606)

superset-frontend/spec/javascripts/views/CRUD/chart/ChartList_spec.jsx

@@ -47,6 +47,7 @@ const mockCharts = [...new Array(3)].map((_, i) => ({
   url: 'url',
   viz_type: 'bar',
   datasource_name: `ds${i}`,
+  thumbnail_url: '/thumbnail',
 }));
 
 fetchMock.get(chartsInfoEndpoint, {
@@ -70,6 +71,9 @@ fetchMock.get(chartsDtasourcesEndpoint, {
   count: 0,
 });
 
+global.URL.createObjectURL = jest.fn();
+fetchMock.get('/thumbnail', { body: new Blob(), sendAsJson: false });
+
 describe('ChartList', () => {
   const mockedProps = {};
   const wrapper = mount(<ChartList {...mockedProps} />, {