CODEWITHSUNDEEP
javascriptunit-testingjestjs
Mateusz Jagiełło
Mateusz Jagiełło

Reputation: 7144

Testing with Jest - reset/clear variables set by tested function and catching console logs

I'm learning writing unit test with Jest.

I use typescript, but it shouldn't be a problem here. Feel free to provide examples with pure JavaScript.

Until now I have function:

const space = String.fromCharCode(0x0020);
const rocket = String.fromCharCode(0xD83D, 0xDE80);
let notified: boolean = false;

export const logHiring = (message: string = "We're hiring!", emoji: string = rocket) => {
    if (!notified) {
        console.info(
            [message, emoji]
                .filter((e) => e)
                .join(space)
        );

        notified = true;
    }
};

Yes, function should log to console just one message per initialization.

And not really working tests:

import {logHiring} from "../index";

const rocket = String.fromCharCode(0xD83D, 0xDE80);

// First test
test("`logHiring` without arguments", () => {
    let result = logHiring();
    expect(result).toBe(`We're hiring! ${rocket}`);
});

// Second test
test("`logHiring` with custom message", () => {
    let result = logHiring("We are looking for employees");
    expect(result).toBe(`We are looking for employees ${rocket}`);
});

// Third test
test("`logHiring` multiple times without arguments", () => {
    let result = logHiring();
    result = logHiring();
    result = logHiring();
    expect(result).toBe(`We're hiring! ${rocket}`);
});

I have two problems:

  1. How can I test console logs? I've tried spyOn without succes.
  2. How can I reset internal (from function) notified variable for each test?

Upvotes: 0

Views: 4236

Answers (1)

Allen
Allen

Reputation: 4789

How can I test console logs? I've tried spyOn without succes.

https://facebook.github.io/jest/docs/en/jest-object.html#jestspyonobject-methodname

const spy = jest.spyOn(console, 'log')
logHiring();
expect(spy).toHaveBeenCalledWith("We're hiring!")

How can I reset internal (from function) notified variable for each test?

export a getter/setter function like

// index.js
export const setNotified = (val) => { notified = val }
export const getNotified = _ => notified

// index.test.js
import { getNotified, setNotified } from '..'
let origNotified = getNotified()
beforeAll(_ => {
  setNotified(/* some fake value here */)
  ...
}
afterAll(_ => {
  setNotified(origNotified)
  ...
}

Upvotes: 1

Related Questions