https://github.com/facebook/react/blob/30b47103d4354d9187dc0f1fb804855a5208ca9f/packages/scheduler/src/Scheduler.js#L180-L185
/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @emails react-core
 */
'use strict';
let Scheduler;
let runWithPriority;
let ImmediatePriority;
let UserBlockingPriority;
let NormalPriority;
let LowPriority;
let IdlePriority;
let scheduleCallback;
let cancelCallback;
let wrapCallback;
let getCurrentPriorityLevel;
let shouldYield;
describe('Scheduler', () => {
  beforeEach(() => {
    jest.resetModules();
    jest.mock('scheduler', () => require('scheduler/unstable_mock'));
    Scheduler = require('scheduler');
    runWithPriority = Scheduler.unstable_runWithPriority;