Javascript mock third-party node library on function call

Question

I'm using sinon and I want to do something very simple, and I cannot find any solution after a lot of searching.

I have class MessageService class looks like this:

import sb from "@azure/service-bus";

    export class MessageService {

        async handleNewMessage() {

            //some code ....

            await sb.delay(5000);

           //some code ....
        }

    }

I want to test the handleNewMessage method , but inside there is call to third party library sb.delay(5000) (that actually sleep for 5s)
I want to replace this function and make it to do nothing .

In my messageService.spec.js file I tried to import it and replace it, but it's not working.

import sb from "@azure/service-bus";

describe('message service', () => {

 beforeEach(() => {
        sinon.stub(sb, 'delay').returns(()=>{});
    });

 afterEach(() => {
        sinon.restore();
    });

it("handleNewMessage should work", async () => {

        //This is call to the real sb.delay function
        await messageServiceMock.handleNewMessage();

    });

})

Is there any way to replace the original class third party function call?

Answer 1

From this comment: https://github.com/sinonjs/sinon/issues/1711#issuecomment-369220753

we're not allowed to modify modules that are imported using import. It looks like imports are read-only views on exports.

So, sinon.stub is not able to modify the imported module.

Take a look at sb.delay implementation:

export function delay<T>(t: number, value?: T): Promise<T> {
  return new Promise(resolve => setTimeout(() => resolve(value), t));
}
//...
export { delay }

Here is the solution:

MessageService.ts :

import * as sb from "@azure/service-bus";

export class MessageService {
  async handleNewMessage() {
    await sb.delay(5000);
  }
}

MessageService.test.ts :

import sinon from "sinon";
import proxyquire from "proxyquire";

describe("message service", () => {
  afterEach(() => {
    sinon.restore();
  });

  it("handleNewMessage should work", async () => {
    const delayStub = sinon.stub().resolves({});
    const { MessageService } = proxyquire("./MessageService.ts", {
      "@azure/service-bus": {
        delay: delayStub,
      },
    });
    const messageServiceMock = new MessageService();
    await messageServiceMock.handleNewMessage();
    sinon.assert.calledWith(delayStub, 5000);
  });
});

Unit test result with 100% coverage:

 message service
    ✓ handleNewMessage should work (1343ms)


  1 passing (1s)

------------------------|----------|----------|----------|----------|-------------------|
File                    |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
------------------------|----------|----------|----------|----------|-------------------|
All files               |      100 |      100 |      100 |      100 |                   |
 MessageService.test.ts |      100 |      100 |      100 |      100 |                   |
 MessageService.ts      |      100 |      100 |      100 |      100 |                   |
------------------------|----------|----------|----------|----------|-------------------|

Source code: https://github.com/mrdulin/mocha-chai-sinon-codelab/tree/master/src/stackoverflow/59234255