第二个expect（fs.writeFile）.toHaveBeenCalledTimes（1）（在describe（'Guid for MPX'）中返回一个错误，因为writeFile被调用了两次。理论上，jest.ResetAllMocks应该处理这个问题，但它没有。

'use strict';
const fs = require('fs').promises;
const path = require('path');

const guidForMpxInvalid = require('../json/guid-for-Mpx-invalid.json')
const data = require('../../../data/sandbox-data-model.json');

jest.mock('fs', () => ({
  promises: {
    writeFile: jest.fn(),
  },
}));

const {
  writeData,
  createGuidForMpx,
  createMpxForGuid,
} = require('../app/transform');

const directoryPath = path.join(__dirname, '../../../wiremock/stubs/mappings');

describe('Write file', () => {
  beforeEach(() => {
    jest.resetAllMocks();
  });

  it('should write a file', async () => {
    const result = await writeData(guidForMpxInvalid, 'guid-for-Mpx-invalid-Mpx.json');
    expect(result).toEqual('guid-for-Mpx-invalid-Mpx.json written');
    expect(fs.writeFile).toHaveBeenCalledTimes(1);
  });
});

describe('Guid for MPX', () => {
  it('should create JSON file for the GUID of a particular MPX', async ()=>{
    const result = await createGuidForMpx(data.Customers[0].guid, data.Customers[0].Customer_Overlays.core.Personal_Details.MPX);
    expect(result).toEqual('guid-for-Mpx-AB123456B.json written');
    expect(fs.writeFile).toHaveBeenCalledTimes(1);
  });
});

被调用的代码：

const writeData = async (data, file) => {
  const directoryPath = path.join(__dirname, '../../wiremock/stubs/mappings');

  try {
    fs.writeFile(`${directoryPath}/${file}`, data);
    return `${file} written`
  } catch (err) {
    return err;
  }
};