redux-saga-testing/jest/01.simple.spec.ts

A no-brainer way of testing your Sagas

import sagaHelper from '../helper';
import 'jest';

// This is the generator / saga you wish to test
function* myGenerator() {
  yield 42;
  yield 43;
  yield 44;
}

describe('When testing a very simple generator (not even a Saga)', () => {
  // You start by overidding the "it" function of your test framework, in this scope.
  // That way, all the tests after that will look like regular tests but will actually be
  // running the generator forward at each step.
  // All you have to do is to pass your generator and call it.
  const it = sagaHelper(myGenerator());

  // This looks very much like a normal "it", with one difference: the function is passed
  // a "result", which is what has been yield by the generator.
  // This is what you are going to test, using your usual testing framework syntax.
  // Here we are using "expect" because we are using Jest, but really it could be anything.
  it('should return 42', result => {
    expect(result).toBe(42);
  });

  // On the next "it", we move the generator forward one step, and test again.
  it('and then 43', result => {
    expect(result).toBe(43);
  });

  // Same here
  it('and then 44', result => {
    expect(result).toBe(44);
  });

  // Now the generator doesn't yield anything, so we can test we arrived at the end
  it('and then nothing', result => {
    expect(result).toBeUndefined();
  });
});