Is worth mentioning that you can do async tests using mocha’s way of handling async code and chai’s assertion style:

it(“should test async code”, done => {
  const newUser = {posts: []};// 3 posts
  myPromise() // returns the user
    .then(user => {
      //expected amount
      const exAmount = newUser.posts.length;
      assert.lengthOf(user.posts, exAmount);
      done();
    })
    .catch( e => done(e) );
});