Jest + Typescript + mock + fs

01-fs.ts

// __mocks__/fs.ts

const promises = {
  readFile: jest.fn()
};

export { // or whatever you've to mock.
  promises
}

02-class.spec.ts

// class.spec.ts

import { mocked } from 'ts-jest/utils';
import { promises } from 'fs';

jest.mock('fs');

describe('Class', () => {
  describe('method', () => {
    beforeEach(() => {
      mocked(promises.readFile as jest.Mock).mockImplementation(() => {
        throw new Error();
      });
    });

    beforeEach(() => {
      mocked(promises.readFile as jest.Mock).mockReturnValueOnce(content);
    });
  });
});