CODEWITHSUNDEEP
node.jsmocha.jssinoneventemitter
Tran B. V. Son
Tran B. V. Son

Reputation: 839

Unit test for Event Emitter Nodejs?

I created a simple class for polling by Event Emitter of Nodejs For example:

import EventEmitter from "events";
import config from "../config";

export class Poller extends EventEmitter {
  constructor(private timeout: number = config.pollingTime) {
    super();
    this.timeout = timeout;
  }

  poll() {
    setTimeout(() => this.emit("poll"), this.timeout);
  }

  onPoll(fn: any) {
    this.on("poll", fn); // listen action "poll", and run function "fn"
  }
}

But I don't know to write the right test for Class. This my unit test 

import Sinon from "sinon";
import { Poller } from "./polling";
import { expect } from "chai";

describe("Polling", () => {
  it("should emit the function", async () => {
    let spy = Sinon.spy();
    let poller = new Poller();

    poller.onPoll(spy);
    poller.poll();

    expect(spy.called).to.be.true;
  });
});

But It always false

  1) Polling
       should emit the function:

      AssertionError: expected false to be true
      + expected - actual

      -false
      +true

Please tell me what's wrong with my test file. Thank you very much !

Upvotes: 0

Views: 581

Answers (1)

hoangdv
hoangdv

Reputation: 16127

You can follow sinon doc

Quick fix

import Sinon from "sinon";
import { Poller } from "./polling";
import { expect } from "chai";
import config from "../config";

describe("Polling", () => {
  it("should emit the function", async () => {
    // create a clock to control setTimeout function
    const clock = Sinon.useFakeTimers();
    let spy = Sinon.spy();
    let poller = new Poller();

    poller.onPoll(spy);
    poller.poll(); // the setTimeout function has been locked

    // "unlock" the setTimeout function with a "tick"
    clock.tick(config.pollingTime + 10); // add 10ms to pass setTimeout in "poll()"

    expect(spy.called).to.be.true;
  });
});

Upvotes: 1

Related Questions