Asynchronous test of vue with mocha

example.ts

import * as Vue from "vue";
import * as assert from "power-assert";

function nextTick() {
  return new Promise((resolve, _) => Vue.nextTick(resolve));
}

describe("vue component tests", function() {
  it("works properly", async function() { // don't use `done` with async function
    const vm = new Vue({ ... });    
    assert(vm.$el.innerHTML === "...");

    vm.$emit("someEvent", { ... });
    await nextTick();

    assert(vm.$el.innerHTML === "...");
  }
});