Improve tests for JavaScript (#3496)

- Upgrade dependencies
    - chai (3.5.0 -> 4.0.1)
    - chai-enzyme (0.6.1 -> 0.7.1)
    - sinon (2.2.0 -> 2.3.2)
- Change extensions from .jsx to .js
- Don't assign `React` to `global`
- Check code format using ESLint

spec/javascript/components/dropdown_menu.test.js

@@ -0,0 +1,97 @@
+import { expect } from 'chai';
+import { shallow, mount } from 'enzyme';
+import sinon from 'sinon';
+import React from 'react';
+import DropdownMenu from '../../../app/javascript/mastodon/components/dropdown_menu';
+import Dropdown, { DropdownTrigger, DropdownContent } from 'react-simple-dropdown';
+
+describe('<DropdownMenu />', () => {
+  const icon = 'my-icon';
+  const size = 123;
+  const action = sinon.spy();
+
+  const items = [
+    { text: 'first item',  action: action, href: '/some/url' },
+    { text: 'second item', action: 'noop' },
+  ];
+  const wrapper = shallow(<DropdownMenu icon={icon} items={items} size={size} />);
+
+  it('contains one <Dropdown />', () => {
+    expect(wrapper).to.have.exactly(1).descendants(Dropdown);
+  });
+
+  it('contains one <DropdownTrigger />', () => {
+    expect(wrapper.find(Dropdown)).to.have.exactly(1).descendants(DropdownTrigger);
+  });
+
+  it('contains one <DropdownContent />', () => {
+    expect(wrapper.find(Dropdown)).to.have.exactly(1).descendants(DropdownContent);
+  });
+
+  it('uses props.size for <DropdownTrigger /> style values', () => {
+    ['font-size', 'width', 'line-height'].map((property) => {
+      expect(wrapper.find(DropdownTrigger)).to.have.style(property, `${size}px`);
+    });
+  });
+
+  it('uses props.icon as icon class name', () => {
+    expect(wrapper.find(DropdownTrigger).find('i')).to.have.className(`fa-${icon}`);
+  });
+
+  it('is not expanded by default', () => {
+    expect(wrapper.state('expanded')).to.be.equal(false);
+  });
+
+  it('does not render the list elements if not expanded', () => {
+    const lis = wrapper.find(DropdownContent).find('li');
+    expect(lis.length).to.be.equal(0);
+  });
+
+  it('sets expanded to true when clicking the trigger', () => {
+    const wrapper = mount(<DropdownMenu icon={icon} items={items} size={size} />);
+    wrapper.find(DropdownTrigger).first().simulate('click');
+    expect(wrapper.state('expanded')).to.be.equal(true);
+  });
+
+  // Error: ReactWrapper::state() can only be called on the root
+  /*it('sets expanded to false when clicking outside', () => {
+    const wrapper = mount((
+      <div>
+        <DropdownMenu icon={icon} items={items} size={size} />
+        <span />
+      </div>
+    ));
+
+    wrapper.find(DropdownTrigger).first().simulate('click');
+    expect(wrapper.find(DropdownMenu).first().state('expanded')).to.be.equal(true);
+
+    wrapper.find('span').first().simulate('click');
+    expect(wrapper.find(DropdownMenu).first().state('expanded')).to.be.equal(false);
+  })*/
+
+  it('renders list elements for each props.items if expanded', () => {
+    const wrapper = mount(<DropdownMenu icon={icon} items={items} size={size} />);
+    wrapper.find(DropdownTrigger).first().simulate('click');
+    const lis = wrapper.find(DropdownContent).find('li');
+    expect(lis.length).to.be.equal(items.length);
+  });
+
+  it('uses the href passed in via props.items', () => {
+    wrapper
+      .find(DropdownContent).find('li a')
+      .forEach((a, i) => expect(a).to.have.attr('href', items[i].href));
+  });
+
+  it('uses the text passed in via props.items', () => {
+    wrapper
+      .find(DropdownContent).find('li a')
+      .forEach((a, i) => expect(a).to.have.text(items[i].text));
+  });
+
+  it('uses the action passed in via props.items as click handler', () => {
+    const wrapper = mount(<DropdownMenu icon={icon} items={items} size={size} />);
+    wrapper.find(DropdownTrigger).first().simulate('click');
+    wrapper.find(DropdownContent).find('li a').first().simulate('click');
+    expect(action.calledOnce).to.equal(true);
+  });
+});