Promise test with Jest

hello.spec.jsx

import React from "react"
import { render, unmountComponentAtNode } from "react-dom"
import { act } from "react-dom/test-utils"

let container = null

beforeEach(() => {
  // setup a DOM element as a render target
  container = document.createElement("div")
  document.body.appendChild(container)
})

afterEach(() => {
  // cleanup on exiting
  unmountComponentAtNode(container)
  container.remove()
  container = null
})

const Hello = () => {
  const promise = Promise.reject("Oh no!")
  return <div>Hello world</div>
}

test("HelloWorld", () => {
  act(() => {
    render(<Hello />, container)
  })
  expect(container.textContent).toBe("Hello world")
})