Can't mock default export in tested file

I'm working on a Typescript project and I'm trying to add tests for functions that are sorting through MongoDB responses to get meaningful results. I've set up an in-memory mock of the database, now I just need to somehow get the test to use this mock database when running tests on the functions in my file.

I have a file called mongoClient.ts that is responsible for this MongoClient object that I need to mock:

import { MongoClient } from 'mongodb';

const client = new MongoClient(`${process.env.MONGO_CONNECT}`);

export default client;

The file that I need to test, called models.ts, imports mongoClient with an ES6 import statement:

import client from '../mongoClient';

In my test I have created a MongoMemoryServer (mongodb-memory-server), and I have made a class to handle the connection to this MongoMemoryServer:

class dbConnection {
  server;
  connection;
  uri;
  async init() {
    this.server = await MongoMemoryServer.create();
    this.uri = await this.server.getUri();
    this.connection = await new MongoClient(this.uri);
    return this.connection;
  }

  connect() {
    this.connection.connect();
  }

  getClient() {
    return this.connection;
  }

  getUri() {
    return this.uri;
  }

  async stopIt() {
    await this.server.stop();
  }
}

I cannot seem to get the models object that I create in the test (with const models = require('../src/models');) to mock its import of 'mongoClient'. I've tried the following:

let mock_db = new dbConnection();
jest.doMock('../src/mongoClient', () => ({
  __es6Module: true,
  default: mock_db.getClient()
}));

I tried to use mock(...) earlier; that throws this error when I run the test:

The module factory of `jest.mock()` is not allowed to reference any out-of-scope variables.

In a beforeAll(...) I am able to fill this DB with dummy information so my functions in models will run correctly, but these functions can't see the mock in-memory database because I can't properly mock the mongoClient file that gets imported at the top of my models.ts. I don't want to have to change any code that isn't in a .test file to accomplish this, but I can't get this test environment to point at my mock in-memory database while running these tests. I must be missing something about the implementation of doMock, and I need some help to fix it.

- -EDIT_1- - I think this might have something to do with the order in which I'm declaring things. The class dbConnection is declared directly under my imports at the top of the test file. Then under that I instantiate the dbConnection class as mockDb and jest.doMock(... like in the example shown above. My tested function seems to be trying to use a mocked import that only contains the following:

{"__es6Module":true}

The error message I'm getting at this point is ERROR --- _get__(...).db is not a function.

The problem with this could be that it's mocking the imported module correctly, but the default export used to mock (mockDb.getClient()) is undefined when it's declared in that doMock statement near the top of the file. I don't know where else to move that doMock, and it breaks if I move it into the top-level beforeAll or into the describe section for these tests or into the test itself.

- -EDIT_2- - Changing __es6Module to __esModule (because the compiled js file looks for __esModule) makes it so that undefined is the contents of the imported class in my code.

The compiled js code has the following at the top:

var __importDefault = (this && this.__importDefault) || function (mod) {
    return (mod && mod.__esModule) ? mod : { "default": mod };
};
const mongoClient_1 = __importDefault(require("../util/mongoClient"));

- -FINAL_EDIT- - I've figured this out, it was an error on my part in how the order of the Jest tests were being executed. The default export client that I was mocking had not been initialized before the tests were being run. This required that I mock the default import in a beforeAll(...) statement inside of each 'describe' block of tests, and in each test I have to instantiate a new models at the start of the test with const models = require(...);. I have working tests now, and everything is good in life ;-)