Question 291666 in Javascript Question posted in
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Constructor mock not working in mocha unit test in Javascript

I am trying to raise an exception for an constructor method of EventHubBufferedProducerClient but its not working as expected. Am I missing something here.

My class method:

import { EventHubBufferedProducerClient } from '@azure/event-hubs';
import { logger } from '../logger';

this.producer = null;
async connect() {
   
    if (this.producer === null) {
      try {
        this.producer = new EventHubBufferedProducerClient(this.connStr, this.eHub);
      } catch (e) {
        logger.error(`Error while connecting to sEHub${this.eHub}`, e);
      }
    }
  }

Below is my test case:

//In before each
 sandbox = sinon.createSandbox();
 eventHubProducer = EventBusProducer('mockEventHubName', 'mockconnectionString');

 it('should log an error if connection fails', async () => {
      const logSpy = sandbox.spy(logger, 'error');
      
      // Force connection failure by throwing an error
      sandbox.stub(EventHubBufferedProducerClient.prototype, 'constructor').throws(new Error('Connection failed'));

      await eventHubProducer.connect();

      expect(eventHubProducer.producer).to.be.null;
      expect(logSpy.calledWith("Error while connecting to sEHub mockEventHubName")).to.be.true;
    });

I am getting below error:

should log an error if connection fails:
     AssertionError: expected EventHubBufferedProducerClient{ …(9) } to be null
      at Context.<anonymous> (EventBusProducer.test.js)
      at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    Finally found the answer after some struggle. In case if anyone encounter such in future the answer may help.

    use the below line in the test case to throw error.

    import * as EventHubModule from '@azure/event-hubs';

 sandbox.stub(EventHubModule, 'EventHubBufferedProducerClient').throws(new Error('Connection failed'));

  2. 0 
    import sinon from 'sinon';
import { expect } from 'chai';
import { EventHubBufferedProducerClient } from '@azure/event-hubs';
import { EventBusProducer } from 'path-to-your-producer'; // Replace with the actual path

describe('EventBusProducer', () => {
  let sandbox;
  let eventHubProducer;

  beforeEach(() => {
    sandbox = sinon.createSandbox();
    eventHubProducer = new EventBusProducer('mockEventHubName', 'mockconnectionString');
  });

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

  it('should log an error if connection fails', async () => {
    const logSpy = sandbox.spy(logger, 'error');

    // Stub the connect method to throw an error
    sandbox.stub(EventHubBufferedProducerClient.prototype, 'connect').throws(new Error('Connection failed'));

    await eventHubProducer.connect();

    expect(eventHubProducer.producer).to.be.null;
    expect(logSpy.calledWith("Error while connecting to sEHub mockEventHubName")).to.be.true;
  });
});

    You are so stubbing the connect method of EventHubBufferedProducerClient, which is invoked when an instance is created. If the connection fails, an error will be thrown, and the catch block in the connect method should report the problem and change this.producer to null.

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