mongodb-memory-server: "MongoMemoryReplSet" in "jest" gives open handle error

If I close the client & await replSet.stop(), jest spits out an error:

Jest did not exit one second after the test run has completed.

This usually means that there are asynchronous operations that weren't stopped in your tests. Consider running Jest with `--detectOpenHandles` to troubleshoot this issue.

If I don’t use a replset, then it works.

describe('MyTests', () => {
  let replSet: MongoMemoryReplSet;
  let client: MongoClient;

  beforeAll(async () => {
    replSet = new MongoMemoryReplSet({
      binary: {
        version: '4.0.5'
      },
      instanceOpts: [{
        storageEngine: 'wiredTiger'
      }],
      autoStart: true,
      debug: true
    });

    await replSet.waitUntilRunning();

    // ... connect to client, etc
  });

  afterAll(async () => {
    await client.close();
    await replSet.stop();
  });

  // ...
});

If I replace the above with just a single mongo server and stop it, it works.