How to properly unit test initialisation of pg-promise via jest.mock / jest.mocked methods?

[filipe-costa]

Currently, I have setup my code as follows:

import pgPromise from "pg-promise";

const pgp = pgPromise();

export const createDBConnection = async () => {
    const db = pgp({
        host: "",
        ssl: false,
        user: "",
        password: "",
        port: 3306,
        max: 25
    });

    try {
        const connection = await db.connect();
        connection.done();
    } catch (err) {
        console.error(err)
    }

    return db;
}

and my test as follows:

import { createDBConnection } from ".";

jest.mock('pg-promise');

describe('db', () => {
    it('initialises with correct parameters', async () => {
        await createDBConnection();
        ...
    });
});

Unfortunately, the test fails with:

TypeError: pgp is not a function

The following works:

import { createDBConnection } from ".";

jest.mock('pg-promise', () => () => jest.fn());

describe('db', () => {
    it('initialises with correct parameters', async () => {
        await createDBConnection();
    });
});

But I am looking to use jest.mocked so I can check that pgp function is called with the correct parameters since these might come from an external configuration.

import pgPromise from "pg-promise";
import { createDBConnection } from ".";

jest.mock('pg-promise');

jest.mocked(pgPromise).mockImplemetation(() => jest.fn()); <- issue with typescript in here

describe('db', () => {
    it('initialises with correct parameters', async () => {
        await createDBConnection();
    });
});

I am using the following library versions:

"pg-promise": "^11.9.0"
"jest": "^29.7.0",
"ts-jest": "^29.2.0",
"typescript": "^5.5.3"

Thanks in advance

[vitaly-t]

We do not cover issues with test frameworks here.