How to mock SQL Server connection pool in node - node.js

Question

I am attempting to mock SQL Server connection pool so that I can test the function of a DAL.
I have a connection pool file
connectionPool.js
const sql = require('mssql');
const log = require('../services/logger');
const config = {
user: process.env.DB_USER,
password: process.env.DB_PASSWORD,
server: process.env.SERVER,
database: process.env.DATABASE
};
const poolPromise = new sql.ConnectionPool(config)
.connect()
.then(pool => {
log.info('Connected to SQL Server');
return pool;
})
.catch(err => {
log.error(err, 'Database connection failed');
});
module.exports = poolPromise;
and I use it in the DAL. Very stripped down, but the essentials are there.
const {poolPromise} = require('./connectionPool');
const getData = async () => {
const pool = await poolPromise;
const request = pool.request()
const result = await request('SELECT * FROM table');
}
This way, the connection pool is only created once per application. (See How can I use a single mssql connection pool across several routes in an Express 4 web application?)
I want to mock the mssql module so that the connection pool function still works. I have tried multiple options. How to mock SQL Server connection pool using Jest? gets me close, but its not quite there.
__mocks/mssql.js
const mockExecute = jest.fn();
const mockInput = jest.fn(() => ({ execute: mockExecute }));
const mockRequest = jest.fn(() => ({ input: mockInput }));
jest.mock('mssql', () => ({
ConnectionPool: jest.fn(() => ({request: mockRequest})),
NVarChar: jest.fn()
}));
const sql = require('mssql');
module.exports = sql;
However I get the error
TypeError: (intermediate value).connect is not a function
17 |
18 | const poolPromise = new sql.ConnectionPool(config)
19 | .connect()
| ^
20 | .then(pool => {
21 | log.info('Connected to SQL Server');
22 | return pool;

Answer 1

This may be a solution.
A bit of refactoring of connectionPool.js
const sql = require('mssql');
const log = require('../services/logger');
const config = {
user: process.env.DB_USER,
password: process.env.DB_PASSWORD,
server: process.env.SERVER,
database: process.env.DATABASE
};
if (process.env.NODE_ENV === 'development') {
config.options = {
encrypt: false,
trustServerCertificate: true
};
}
const connectionPool = new sql.ConnectionPool(config);
const poolPromise = connectionPool
.connect()
.then(pool => {
log.info('Connected to MSSQL');
return pool;
})
.catch(err => {
log.error(err, 'Database connection failed');
});
module.exports = poolPromise;
Then in /__mocks__/mssql.js
'use strict';
const mockExecute = jest.fn();
const mockInput = jest.fn().mockReturnValue({ execute: mockExecute });
const mockQuery = jest.fn().mockReturnValue({recordset: 'Mock data'});
const mockRequest = jest.fn().mockReturnValue({
input: mockInput,
query: mockQuery
});
const mockTransaction = jest.fn().mockImplementation(() => {
return {
begin: callback => callback(),
commit: jest.fn(),
rollback: jest.fn()
};
});
const mockConnect = jest.fn().mockImplementation(() => {
return Promise.resolve({ transaction: mockTransaction });
});
jest.mock('mssql', () => ({
ConnectionPool: jest.fn().mockReturnValue({
request: mockRequest,
connect: mockConnect
}),
Request: mockRequest,
NVarChar: jest.fn()
}));
const mssql = require('mssql');
module.exports = mssql;
It appears to work, but I am not sure if it is correct