[explore] Improved time filters controls (#3371)

* Improved time filters controls

* lint

* Fix coverage

* Allow empty dates

superset/assets/spec/javascripts/components/PopoverSection_spec.jsx

@@ -0,0 +1,34 @@
+import React from 'react';
+import { expect } from 'chai';
+import { describe, it } from 'mocha';
+import { shallow } from 'enzyme';
+
+import PopoverSection from '../../../javascripts/components/PopoverSection';
+
+describe('PopoverSection', () => {
+  const defaultProps = {
+    title: 'Section Title',
+    isSelected: true,
+    onSelect: () => {},
+    info: 'info section',
+    children: <div />,
+  };
+
+  let wrapper;
+  const factory = (overrideProps) => {
+    const props = Object.assign({}, defaultProps, overrideProps || {});
+    return shallow(<PopoverSection {...props} />);
+  };
+  beforeEach(() => {
+    wrapper = factory();
+  });
+  it('renders', () => {
+    expect(React.isValidElement(<PopoverSection {...defaultProps} />)).to.equal(true);
+  });
+  it('is show an icon when selected', () => {
+    expect(wrapper.find('.fa-check')).to.have.length(1);
+  });
+  it('is show no icon when not selected', () => {
+    expect(factory({ isSelected: false }).find('.fa-check')).to.have.length(0);
+  });
+});