get value from a Promise for unit-testing

Question

I have a method inside a class calculating the sum of 2 parameters that returns a Promise (a must):

module.exports = class Sum {
  sum(a, b) {
    let c = a + b;
    const myPromise = new Promise(function(myResolve) {
      setTimeout(function(){ myResolve(c); }, 100);
    });
    return myPromise;
  }
}

I use Jasmine framework to unit-test

const MyLocalVariable1 = require('../src/sum'); 
describe('CommonJS modules', () => {
  it('should import whole module using module.exports = sum;', async () => {
    const result = new MyLocalVariable1();
    expect(result.sum(4, 5).then(function(value) {
      return value;
    })).toBe(9);
  });
}

The first expression is what we want to test:

result.sum(4, 5).then(function(value) {
  return value;
})

and the second one is the expected value:

toBe(9)

But how can I get a value from the first expression, because it's a Promise, and expected value of it is [object Promise]. Thanks in advance

Answer 1

To drive Konrad's point home, you can do the following:

it('should import whole module using module.exports = sum;', async () => {
    const result = new MyLocalVariable1();
    const answer = await result.sum(4, 5);
    expect(answer).toBe(9);
  });

Or the following:

// add done callback to tell Jasmine when you're done with the unit test
it('should import whole module using module.exports = sum;', (done) => {
    const result = new MyLocalVariable1();
    result.sum(4, 5).then(answer => {
      expect(answer).toBe(9);
      done();
   });

  });