Redux Saga Test Plan

Test Redux Saga with an easy plan.

Redux Saga Test Plan makes testing sagas a breeze. Whether you need to test exact effects and their ordering or just test your saga put's a specific action at some point, Redux Saga Test Plan has you covered.

Redux Saga Test Plan aims to embrace both unit testing and integration testing approaches to make testing your sagas easy.

Integration Testing

Requires global Promise to be available

One downside to unit testing sagas is that it couples your test to your implementation. Simple reordering of yielded effects in your saga could break your tests even if the functionality stays the same. If you're not concerned with the order or exact effects your saga yields, then you can take a integrative approach, testing the behavior of your saga when run by Redux Saga. Then, you can simply test that a particular effect was yielded during the saga run. For this, use the expectSaga test function.

Simple Example

Import the expectSaga function and pass in your saga function as an argument. Any additional arguments to expectSaga will become arguments to the saga function. The return value is a chainable API with assertions for the different effect creators available in Redux Saga.

In the example below, we test that the userSaga successfully puts a RECEIVE_USER action with the fakeUser as the payload. We call expectSaga with the userSaga and supply an api object as an argument to userSaga. We assert the expected put effect via the put assertion method. Then, we call the dispatch method with a REQUEST_USER action that contains the user id payload. The dispatch method will supply actions to take effects. Finally, we start the test by calling the run method which returns a Promise. Tests with expectSaga will always run asynchronously, so the returned Promise resolves when the saga finishes or when expectSaga forces a timeout. If you're using a test runner like Jest, you can return the Promise inside your Jest test so Jest knows when the test is complete.

import { call, put, take } from 'redux-saga/effects';
import { expectSaga } from 'redux-saga-test-plan';

function* userSaga(api) {
  const action = yield take('REQUEST_USER');
  const user = yield call(api.fetchUser, action.payload);

  yield put({ type: 'RECEIVE_USER', payload: user });
}

it('just works!', () => {
  const api = {
    fetchUser: id => ({ id, name: 'Tucker' }),
  };

  return expectSaga(userSaga, api)
    // Assert that the `put` will eventually happen.
    .put({
      type: 'RECEIVE_USER',
      payload: { id: 42, name: 'Tucker' },
    })

    // Dispatch any actions that the saga will `take`.
    .dispatch({ type: 'REQUEST_USER', payload: 42 })

    // Start the test. Returns a Promise.
    .run();
});

Mocking with Providers

expectSaga runs your saga with Redux Saga, so it will try to resolve effects just like Redux Saga would in your application. This is great for integration testing, but sometimes it can be laborious to bootstrap your entire application for tests or mock things like server APIs. In those cases, you can use providers which are perfect for mocking values directly with expectSaga. Providers are similar to middleware that allow you to intercept effects before they reach Redux Saga. You can choose to return a mock value instead of allowing Redux Saga to handle the effect, or you can pass on the effect to other providers or eventually Redux Saga.

expectSaga has two flavors of providers, static providers and dynamic providers. Static providers are easier to compose and reuse, but dynamic providers give you more flexibility with non-deterministic effects. Here is one example below using static providers. There are more examples of providers in the docs.

import { call, put, take } from 'redux-saga/effects';
import { expectSaga } from 'redux-saga-test-plan';
import * as matchers from 'redux-saga-test-plan/matchers';
import { throwError } from 'redux-saga-test-plan/providers';
import api from 'my-api';

function* userSaga() {
  try {
    const action = yield take('REQUEST_USER');
    const user = yield call(api.fetchUser, action.payload);
    const pet = yield call(api.fetchPet, user.petId);

    yield put({
      type: 'RECEIVE_USER',
      payload: { user, pet },
    });
  } catch (e) {
    yield put({ type: 'FAIL_USER', error: e });
  }
}

it('fetches the user', () => {
  const fakeUser = { name: 'Jeremy', petId: 20 };
  const fakeDog = { name: 'Tucker' };

  return expectSaga(userSaga, api)
    .provide([
      [call(api.fetchUser, 42), fakeUser],
      [matchers.call.fn(api.fetchPet), fakeDog],
    ])
    .put({
      type: 'RECEIVE_USER',
      payload: { user: fakeUser, pet: fakeDog },
    })
    .dispatch({ type: 'REQUEST_USER', payload: 42 })
    .run();
});

it('handles errors', () => {
  const error = new Error('error');

  return expectSaga(userSaga, api)
    .provide([
      [matchers.call.fn(api.fetchUser), throwError(error)],
    ])
    .put({ type: 'FAIL_USER', error })
    .dispatch({ type: 'REQUEST_USER', payload: 42 })
    .run();
});

Notice we pass in an array of tuple pairs (or array pairs) that contain a matcher and a fake value. You can use the effect creators from Redux Saga or matchers from the redux-saga-test-plan/matchers module to match effects. The bonus of using Redux Saga Test Plan's matchers is that they offer special partial matchers like call.fn which matches by the function without worrying about the specific args contained in the actual call effect. Notice in the second test that we can also simulate errors with the throwError function from the redux-saga-test-plan/providers module. This is perfect for simulating server problems.

Example with Reducer

One good use case for integration testing is testing your reducer too. You can hook up your reducer to your test by calling the withReducer method with your reducer function.

import { call, select, take } from 'redux-saga/effects';
import { expectSaga } from 'redux-saga-test-plan';

const HAVE_BIRTHDAY = 'HAVE_BIRTHDAY';
const UPDATE_DOG = 'UPDATE_DOG';

const initialState = {
  dog: {
    name: 'Tucker',
    age: 11,
  },
};

function reducer(state = initialState, action) {
  if (action.type === HAVE_BIRTHDAY) {
    return {
      ...state,
      dog: {
        ...state.dog,
        age: state.dog.age + 1,
      },
    };
  }

  return state;
}

const getDog = state => state.dog;

function* saga(api) {
  yield take(UPDATE_DOG);
  const dog = yield select(getDog);
  yield call(api.updateDog, dog);
}

it('handles reducers', () => {
  const api = { updateDog() {} };

  return expectSaga(saga, api)
    .withReducer(reducer)

    .call(api.updateDog, {
      name: 'Tucker',
      age: 12,
    })

    .dispatch({ type: HAVE_BIRTHDAY })
    .dispatch({ type: UPDATE_DOG })

    .run();
});

Unit Testing

If you want to ensure that your saga yields specific types of effects in a particular order, then you'll want to use the testSaga function. Here's a simple example:

import { testSaga } from 'redux-saga-test-plan';

function identity(value) {
  return value;
}

function* mainSaga(x, y) {
  const action = yield take('HELLO');

  yield put({ type: 'ADD', payload: x + y });
  yield call(identity, action);
}

const action = { type: 'TEST' };

it('works with unit tests', () => {
  testSaga(mainSaga, 40, 2);
    // advance saga with `next()`
    .next()

    // assert that the saga yields `take` with `'HELLO'` as type
    .take('HELLO')

    // pass back in a value to a saga after it yields
    .next(action)

    // assert that the saga yields `put` with the expected action
    .put({ type: 'ADD', payload: 42 })

    .next()

    // assert that the saga yields a `call` to `identity` with
    // the `action` argument
    .call(identity, action)

    .next()

    // assert that the saga is finished
    .isDone();
});

Introduction