setup.js

const path = require('path');
const fs = require('fs');
const MongodbMemoryServer = require('mongodb-memory-server');
const globalConfigPath = path.join(__dirname, 'globalConfig.json');

const mongod = new MongodbMemoryServer.default({
  instance: {
    dbName: 'jest'
  },
  binary: {
    version: '3.2.18'
  }
});

module.exports = async function() {
  const mongoConfig = {
    mongoDBName: 'jest',
    mongoUri: await mongod.getUri(),//mongod.getConnectionString(),
    useUnifiedTopology: true,
    useFindAndModify: false
  };

  // Write global config to disk because all tests run in different contexts.
  fs.writeFileSync(globalConfigPath, JSON.stringify(mongoConfig));
  console.log('Config is written');

  // Set reference to mongod in order to close the server during teardown.
  global.__MONGOD__ = mongod;
  process.env.MONGO_URL = mongoConfig.mongoUri;
};