Code Example for Testing a Redux Saga with Mocha

requestPostList.js

import { push } from 'react-router-redux';
import { takeLatest, call, put } from 'redux-saga/effects';
import config from '../../../config/client';
import { REQUEST_POST_LIST } from '../actions';
import updatePostList from '../actions/updatePostList';
import fetchPostList from './utils/fetchPostList';
import trackPageViewWithGoogleAnalytics from '../actions/trackPageViewWithGoogleAnalytics';
import trackPageViewWithIvw from '../actions/trackPageViewWithIvw';

export function *requestPostList({ threadId, page }) {
    let data;
    try {
        data = yield call(fetchPostList, threadId, page);
    } catch (e) {
        yield put(push(`${config.mountPoint}/error/500.html`));
        return;
    }
    yield put(updatePostList(data));
    yield put(trackPageViewWithGoogleAnalytics());
    yield put(trackPageViewWithIvw());
}

export default function *() {
    yield takeLatest(REQUEST_POST_LIST, requestPostList);
}

requestPostListTest.js

import mockery from 'mockery';
import { push } from 'react-router-redux';
import { takeLatest, call, put } from 'redux-saga/effects';
import { REQUEST_POST_LIST } from 'src/shared/redux/actions';
import updatePostList from 'src/shared/redux/actions/updatePostList';
import trackPageViewWithGoogleAnalytics from 'src/shared/redux/actions/trackPageViewWithGoogleAnalytics';
import trackPageViewWithIvw from 'src/shared/redux/actions/trackPageViewWithIvw';
import requestPostListWatcher, { requestPostList } from 'src/shared/redux/sagas/requestPostList';
import fetchPostList from 'src/shared/redux/sagas/utils/fetchPostList';

describe('[shared/redux/sagas/requestPostList]', () => {
    describe('When I instantiate the “go to page” saga generator', () => {
        let generator;
        beforeEach(() => generator = requestPostListWatcher());
        describe('and I call its “next” method', () => {
            let result;
            beforeEach(() => result = generator.next());
            describe('the value returned by the generator', () => {
                it('is a redux-saga “take latest” of the “go to page” action with the argument I passed in', () => {
                    result.value.should.deep.equal(takeLatest(REQUEST_POST_LIST, requestPostList));
                });
            });
        });
    });
    describe('When I instantiate the “go to page” generator', () => {
        let generator;
        beforeEach(() => generator = requestPostList({ threadId: 666, page: 7 }));
        describe('and I call its “next” method', () => {
            let next;
            beforeEach(() => next = generator.next());
            describe('the “next” value', () =>
                it('is a call to the “fetch post list” function with the arguments I provided', () =>
                    next.value.should.deep.equal(call(fetchPostList, 666, 7))
                )
            );
            describe('and I call “next” again with some data', () => {
                beforeEach(() => next = generator.next('qux'));
                describe('the “next” value', () =>
                    it('is a call to “put” of redux-saga with a “update post list” action with my data', () =>
                        next.value.should.deep.equal(put(updatePostList('qux')))
                    )
                );
                describe('and I call “next” again', () => {
                    beforeEach(() => next = generator.next());
                    describe('the “next” value', () =>
                        it('is a call to “put” with a “track page view with Google Analytics” action', () =>
                            next.value.should.deep.equal(put(trackPageViewWithGoogleAnalytics()))
                        )
                    );
                    describe('and I call “next” again', () => {
                        beforeEach(() => next = generator.next());
                        describe('the “next” value', () =>
                            it('is a call to “put” with a “track page view with IVW” action', () =>
                                next.value.should.deep.equal(put(trackPageViewWithIvw()))
                            )
                        );
                    });
                });
            });
        });
    });
    describe(
        'When I instantiate the “go to page” generator, ' +
        'rigged to throw an error when trying to fetch data', () => {
        let generator;
        beforeEach(() => {
            mockery.enable({
                useCleanCache: true,
                warnOnUnregistered: false
            });
            mockery.registerMock('redux-saga/effects', {
                takeLatest,
                call() { throw Error('ZOMG!'); },
                put
            });
            mockery.registerMock('../../../config/client', {
                mountPoint: '/my-mount-point'
            });
            const riggedrequestPostList = require('../../../../src/shared/redux/sagas/requestPostList').requestPostList;
            generator = riggedrequestPostList({ threadId: 666, page: 7 });
        });
        describe('and I call its “next” method', () => {
            let next;
            beforeEach(() => next = generator.next());
            describe('the “next” value', () =>
                it('is a call to “put” of redux-saga with a “push” action with an error URL', () =>
                    next.value.should.deep.equal(put(push('/my-mount-point/error/500.html')))
                )
            );
        });
        afterEach(() => {
            mockery.deregisterAll();
            mockery.disable();
        });
    });
});