I'm trying to use mock-fs to unit test code which uses ES6 dynamic imports.

There seems to be an unexpected coupling between tests when I'm using dynamic imports, even though I call restore() after each test. It appears as though fs.readFile() behaves as expected between tests (no coupling), but await import() has coupling (it returns the result from the previous test).

I've created a minimal Jest test case that reproduces the issue. The tests pass individually, but not when run together. I notice that if I change the directory value so it's different between each test, then they pass together.

Can you help me understand why this doesn't work, whether it's a bug, and what I should do here?

import path from 'path';
import { promises as fs } from 'fs';
import mockFs from 'mock-fs';

const fsMockModules = {
  node_modules: mockFs.load(path.resolve(__dirname, '../node_modules')),
};

describe('Reproduce dynamic import coupling between tests', () => {
  afterEach(() => {
    mockFs.restore();
  });
  it('first test', async () => {
    const directory = 'some/path';
    mockFs({
      ...fsMockModules,
      [directory]: {
        'index.js': ``,
      },
    });
    await import(path.resolve(`${directory}/index.js`));
    //not testing anything here, just illustrating the coupling for next test
  });
  it('second tests works in isolation but not together with first test', async () => {
    const directory = 'some/path';
    mockFs({
      ...fsMockModules,
      [directory]: {
        'index.js': `export {default as migrator} from './migrator.js';`,
        'migrator.js':
          'export default (payload) => ({...payload, xyz: 123});',
      },
    });
    const indexFile = await fs.readFile(`${directory}/index.js`, 'utf-8');
    expect(indexFile.includes('export {default as migrator}')).toBe(true);
    const migrations = await import(path.resolve(`${directory}/index.js`));
    expect(typeof migrations.migrator).toBe('function');
  });
});