Sinon Stub not working with AWS Parameter store (NodeJS)

Question

I am trying to stub a call to the aws parameter store (PS). But even though I added the stub in multiple ways it always makes the actual call to aws PS.

the method I am trying to test

function getParamsFromParamterStore() {
    return ssm.getParametersByPath(query).promise();
}

One of the stub method I tried

var ssm = new AWS.SSM();
stub1 = sinon.stub(ssm, 'getParametersByPath').returns({promise: () => {}});
moduleName.__get__('getParamsFromParamterStore')();

But this actually makes the call to PS.

Note: since this is a private function (not exported) I am using rewire to access it.

Answer 1

Here is the unit test solution:

index.js:

const AWS = require('aws-sdk');
const ssm = new AWS.SSM();

function getParamsFromParamterStore(query) {
  return ssm.getParametersByPath(query).promise();
}

index.test.js:

const rewire = require('rewire');
const sinon = require('sinon');
const { expect } = require('chai');
const mod = rewire('./');

describe('60447015', () => {
  it('should pass', async () => {
    const ssmMock = { getParametersByPath: sinon.stub().returnsThis(), promise: sinon.stub().resolves('mock data') };
    const awsMock = {
      SSM: ssmMock,
    };
    mod.__set__('ssm', awsMock.SSM);
    const actual = await mod.__get__('getParamsFromParamterStore')('query');
    expect(actual).to.be.eq('mock data');
    sinon.assert.calledWithExactly(ssmMock.getParametersByPath, 'query');
    sinon.assert.calledOnce(ssmMock.promise);
  });
});

Unit test results with 100% coverage:

  60447015
    ✓ should pass


  1 passing (30ms)

----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------|---------|----------|---------|---------|-------------------
All files |     100 |      100 |     100 |     100 |                   
 index.js |     100 |      100 |     100 |     100 |                   
----------|---------|----------|---------|---------|-------------------