How can I export an LWC function that's declared within a constructor?

Question

I have a function that is declared within my default class (constructor) that I would like to export to a Jest test suite. Is this possible?

testLWC.js

import { LightningElement } from 'lwc';

export default class JMRTestLWC extends LightningElement {
   sum(a, b) {
      return a + b;
   }
}

testLWC.test.js

import { sum } from 'c/jMRTestLWC'

describe('Addition Suite.', () => {
    test('Properly sum two numbers.', () => {
        const num = 1+2;
        expect(sum(1,2)).toBe(3);
    })
})

Answer 1

In order to use a method, you must expose it as a public method. I wrote a unit test using your code, and it ended up looking like this:

---

import { api, LightningElement } from 'lwc';

export default class Q361000 extends LightningElement {
    @api sum(a, b) {
        return a + b;
    }
}

---

import { createElement } from 'lwc';
import Q361000 from '../q361000';

describe('c-q361000', () =>{
    it('sums correctly', () =>{
        const element = createElement('c-q361000', { is: Q361000 });
        document.body.appendChild(element);
        expect(element.sum(1,2)).toBe(3);
    })
})