old_contents: // component test
  import jsdom from "mocha-jsdom";
  import assert from "assert";
  import React from "react";
  import ReactDOM from "react-dom";
  import ReactTestUtils from "react-addons-test-utils";
  
  import HelloWorld from "../src/components/HelloWorld.jsx";
  
  describe("HelloWorld component", () => {
  
    jsdom();
  
    it("should exist", () => {
      assert.ok( !!HelloWorld );
    });
  
    it("should be react element", () => {
      assert.ok( ReactTestUtils.isElement(<HelloWorld />),
        "is not a react element" );
    });
  
    describe("rendering", () => {
  
      it("should display 'text' prop in DOM somehow", () => {
        const container = document.createElement("div");
        ReactDOM.render(<HelloWorld text="TEST" />, container);
        assert.ok( /TEST/.test(container.innerHTML), "It don't displays 'text' prop in DOM");
      });
  
    });
  
  });
  
new_contents: // component test
  import jsdom from "mocha-jsdom";
  import assert from "assert";
  import React from "react";
  import ReactDOM from "react-dom";
  import ReactTestUtils from "react-addons-test-utils";
  
  import HelloWorld from "../src/components/HelloWorld.jsx";
  
  describe("HelloWorld component", () => {
  
    jsdom();
  
    it("should exist", () => {
      expect(HelloWorld).to.exist;
    });
  
    it("should be react element", () => {
      ReactTestUtils.isElement(<HelloWorld />).should.be.ok;
    });
  
    describe("rendering", () => {
  
      it("should display 'text' prop in DOM somehow", () => {
        const container = document.createElement("div");
        ReactDOM.render(<HelloWorld text="TEST" />, container);
        container.innerHTML.should.contain("TEST");
      });
  
    });
  
  });
  
subject: Rewrite test cases to chai