Use sinon to mock node-mssql

[cklat]

Describe the bug

I'm trying to mock a database connection for which I'm using the tedious node-mssql library (https://github.com/tediousjs/node-mssql)

More concretely, I'm trying to stub the ConnectionPool method of the library as follows (with mocha and chai):

mockDB.test.ts

import * as sinon from 'sinon';
import * as mssql from 'mssql';

describe('EmployeeDiscountController', function () {
   beforeEach(async function() {
    sinon.stub(mssql, 'ConnectionPool').returns({
      ConnectionPool: sinon.stub().returns({
        request: () => {},
        connect: () => {}
      })
    });
  });
});

(I skipped all the unnecessary parts in the code.)

Unfortunately, I get the following error:

TypeError: Descriptor for property ConnectionPool is non-configurable and non-writable
    at assertValidPropertyDescriptor (node_modules\sinon\lib\sinon\stub.js:138:15)
    at Function.stub (node_modules\sinon\lib\sinon\stub.js:89:5)
    at Object.stub (node_modules\sinon\lib\sinon\sandbox.js:389:39)

Do you know why this is?

I saw a PR that would resolve this issue but as I am using the latest sinon version (15.2.0) this problem seems to persist for me.

Is it advisable to even use sinon to mock such packages? I don't very little experience in writing tests and am actually using sinon the first time.

Thank you very much for your help!

[fatso83]

Hi, this is is more less exactly what I covered in this new article I just wrote on different approaches to testing. You can see if you find your answer there: #2540

Basically, the value you are trying to stub is not a value, but a kind of getter. You can read about these here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty

My article covers different approaches on how you can attach this (I cover 3 very different approaches, from tool configuration, external loaders and through exposing your code).