Testing a static method from a singleton in Jest (Node.js)

Question

// tester.js
class Tester {
  static loggit(text) {
    return text;
  }
}

module.exports = new Tester();

When testing this singleton in Node.js using Jest

// tester.spec.js
const Tester = require('./tester.js');

describe('Tester testing', () => {
  it('logs it', () => {
    expect(Tester.loggit('test')).toEqual('test');
  });
});

When running the test, I get an error saying "encountered a declaration exception. TypeError: Tester.loggit is not a function"

I tried using jest.requireActual to resolve it, but it's not fixing the error.

I don't want to export the class itself as it will be a singleton in my app.

Any input will be helpful.

Static method in a singleton? Why?..

Estus Flask
– Estus Flask

2019-03-19 21:18:39 +00:00
Commented Mar 19, 2019 at 21:18 — Estus Flask
– Estus Flask, Commented Mar 19, 2019 at 21:18

Jonas Wilms · Accepted Answer · 2019-03-19 21:19:44Z

3

You want to export the class itself, not an instance of the class:

module.exports = Tester;

And if just have static methods, you could just export an object:

 module.exports = {
  loggit(it) { return it; },
 };

If you really want to have both a singleton and static properties (what purpose should that serve?!), then you can get the class from an instance using the constructor property:

 (new Tester).constructor.loggit("test")

edited Mar 19, 2019 at 21:19

answered Mar 19, 2019 at 21:13

Jonas Wilms

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