[explore] fix missing CacheLabel (#4326)

Also adding a basic unit test.

superset/assets/spec/javascripts/explore/components/ExploreChartHeader_spec.jsx

@@ -0,0 +1,40 @@
+import React from 'react';
+import { expect } from 'chai';
+import { describe, it } from 'mocha';
+import { shallow } from 'enzyme';
+
+import ExploreChartHeader from '../../../../javascripts/explore/components/ExploreChartHeader';
+import ExploreActionButtons from '../../../../javascripts/explore/components/ExploreActionButtons';
+import EditableTitle from '../../../../javascripts/components/EditableTitle';
+
+const mockProps = {
+  actions: {},
+  can_overwrite: true,
+  can_download: true,
+  isStarred: true,
+  slice: {},
+  table_name: 'foo',
+  form_data: {},
+  timeout: 1000,
+  chart: {
+    queryResponse: {},
+  },
+};
+
+describe('ExploreChartHeader', () => {
+  let wrapper;
+  beforeEach(() => {
+    wrapper = shallow(<ExploreChartHeader {...mockProps} />);
+  });
+
+  it('is valid', () => {
+    expect(
+      React.isValidElement(<ExploreChartHeader {...mockProps} />),
+    ).to.equal(true);
+  });
+
+  it('renders', () => {
+    expect(wrapper.find(EditableTitle)).to.have.lengthOf(1);
+    expect(wrapper.find(ExploreActionButtons)).to.have.lengthOf(1);
+  });
+});