Spying on redux-saga effects

spy-on-effects.js

// In test file

const spy = effectSpy(generator)
  .next('init')
  .next('getToken', token) // name and pass in yield values
  .next('getUpdatedFooBars', fooBars)
  .next('putFooBars');

// in beforeEach
mySpyRun = spy.run({
  getToken: 'invalid-token' // accepts overrides
});

// in `it` statement
expect(mySpyRun.getToken.value).to.deep.equal(select(getToken))
expect(mySpyRun.putFooBars.value)
  .to.deep.equal(put(fooBarsAction, fooBars))


// In test utils file

export const effectRunner = function effectRunner(generator) {
  const steps = [];

  const next = function (name, value) {
    steps.push({ name, value });
    return { next, run };
  };

  const run = function (overrides = {}) {
    let g;
    const stepOutput = {};
    let prevValue;

    steps.forEach(({ name, value }) => {
      if (g) {
        stepOutput[name] = g.next(prevValue);
        prevValue = overrides[name] || value;
        return;
      }

      g = generator(value);
    });

    return stepOutput;
  };

  return { next, run };
};