The callback in database authentication caused error when executing model unit test file

When doing model unit test in the nodejs 12.15/sequelize 5.21 app with jest 25.x, I notice there is some error message about the callback for the db.authenticate():

●  Cannot log after tests are done. Did you forget to wait for something async in your test?
    Attempted to log "DB connection has been established successfully.".

      32 | db
      33 |     .authenticate()
    > 34 |     .then(() => {
         |           ^
      35 |        console.log('DB connection has been established successfully.');
      36 |         // The event will be called when a client is connected.
      37 |

      at CustomConsole.log (node_modules/@jest/console/build/CustomConsole.js:186:10)
      at startup/db.js:34:11
      at tryCatcher (node_modules/bluebird/js/release/util.js:16:23)
      at Promise._settlePromiseFromHandler (node_modules/bluebird/js/release/promise.js:547:31)
      at Promise._settlePromise (node_modules/bluebird/js/release/promise.js:604:18)
      at Promise._settlePromise0 (node_modules/bluebird/js/release/promise.js:649:10)
      at Promise._settlePromises (node_modules/bluebird/js/release/promise.js:729:18)
      at _drainQueueStep (node_modules/bluebird/js/release/async.js:93:12)
      at _drainQueue (node_modules/bluebird/js/release/async.js:86:9)
      at Async.Object.<anonymous>.Async._drainQueues (node_modules/bluebird/js/release/async.js:102:5)

The code causing the error is for establishing the connection to database:

const Sql = require("sequelize");
const db = new Sql('my_db', 'postgres', `${process.env.DB_PASSWORD}`, {
        host: 'localhost',
        dialect: 'postgres',
        port:5432,
    } );    

db.authenticate()
  .then(() => {
       console.log('DB connection has been established successfully.');  //<<<<===this callback caused error

    })
    .catch(err => {
        console.error('Unable to connect to the database:', err);
    });

The error occurs for every model.test.js file executed. The db connection is established at top level index.js and there is no way to do a async/await except the callback. Since this is not a real bug in the code, how to make the error disappear?