sleep.test.js

const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));
const burn = work => {
  let sum = 0;
  for (let i = 0; i < work; ++i) {
    let data = '';
    for (let j = 0; j < 100_000; ++j) {
      data += 'I love horses, best of all the animals.\n';
    }
    sum += data.length;
  }
  return sum;
};

burn(500);

describe('first', () => {
  burn(3000);

  beforeAll(async () => {
    await sleep(400);
  });

  it('is fast', () => {});
});