using sinon stub to test a method on an object

Question

I want to test a function inside an object. The code, lets call it someFile.js, is structured as below.

import someService from 'a-location';

const val = someService.getVal();

const AnObject = {
  someMethod() {
   if(val) //dosomething
  }
}

export default AnObject;

In the test file, I have code as below

import someService from 'a-location';
import AnObject from 'someFile';

describe("description", function(){
  it('more description', function() {
    sinon.stub(someService, 'getVal').returns('my-val');
    AnObject.someMethod();
})
})

I was hoping to receive 'my-val' when someService.getVal() is called in the someFile.js but it isn't working as expected. What am I doing wrong?

Answer 1

You should use import() to import the AnObject from someFile dynamically after stubbing.

E.g.

some-file.ts:

import someService from './a-location';

const val = someService.getVal();

const AnObject = {
  someMethod() {
    console.log('val: ', val);
  },
};

export default AnObject;

a-location.ts:

const someService = {
  getVal() {
    return 'real val';
  },
};

export default someService;

some-file.test.ts:

import sinon from 'sinon';
import someService from './a-location';

describe('description', () => {
  it('more description', async () => {
    sinon.stub(someService, 'getVal').returns('my-val');
    const AnObject = (await import('./some-file')).default;
    AnObject.someMethod();
  });
});

Test result:

  description
val:  my-val
    ✓ more description


  1 passing (8ms)

As you can see, the val is my-val which is a stubbed value.