* Mocha + ES6
** Setup
Run the following shell commands:
#+BEGIN_SRC sh
  yarn init
  yarn add --dev mocha chai babel-cli babel-preset-es2015 babel-preset-flow babel-plugin-transform-class-properties flow-typed flow-bin
#+END_SRC

Open up =package.json= and set your test script to the following:
=mocha --watch --compilers js:babel-core/register=

Create a =.babelrc= file in the project directory:
#+BEGIN_SRC js
  {
    "presets": ["flow", "es2015"],
    "plugins": ["transform-class-properties"]
  }
#+END_SRC
** Example sources
#+BEGIN_SRC js
  // test/main.test.js
  //@flow
  import { expect } from 'chai';

  import Main from '../src/main';

  describe('Main', () => {

      it('should be a class', () => {
          expect(new Main()).to.not.equal(undefined);
      });

  });
#+END_SRC

#+BEGIN_SRC js
  // src/main.js
  //@flow
  export default class Main {
      constructor() {
      }
  }
#+END_SRC
** Example output
#+BEGIN_SRC sh
  > yarn test

    Main
      ✓ should be a class


    1 passing (12ms)
#+END_SRC

** Setting up Flow and Flow-typed
Flow-typed creates library definitions for third-party code (like Mocha) so Flow's able to check your tests. To set it up, first initialize Flow in your project and then install library definitions by running the following commands:

#+BEGIN_SRC sh
  > yarn flow init
  > yarn flow-typed install
#+END_SRC

*** Example Usage
#+BEGIN_SRC sh
  > yarn flow
  No errors!
  ✨ Done in 3.34s.
#+END_SRC