redux-saga-jest

Helper library for testing redux sagas in jest.

redux-saga-jest extends expect with useful matchers that let you easily validate saga effects, and binds your sagas to test (it alias is also available) and expect functions, providing an easy way to control saga's execution.

Installation

Install redux-saga-jest using yarn:

$ yarn add redux-saga-jest --dev

Or via npm:

$ npm install redux-saga-jest --save-dev

Getting Started

Let's start writing tests for a simple generator (yes, you can use redux-saga-jest to test plain generators, too):

function* simpleGenerator() {
    let msg, n = 1
    while (n < 3) {
        msg = yield msg || n
        n++
    }
}

You will need to import runSaga function from redux-saga-jest and call it with your generator's iterator as an argument. It'll return an object containing enhanced test, it and expect functions. redux-saga-jest will iterate over the generator when you call it and provide the yielded value and done flag as first argument in your test function.

import runSaga from 'redux-saga-jest'
 
describe('simpleGenerator', () => {
    const { it, expect } = runSaga(simpleGenerator())
 
    it('should yield 1', ({ value }) => {
        expect(value).toBe(1)
    })
 
    it('then should yield 2', ({ value }) => {
        expect(value).toBe(2)
    })
 
    it('then should finish', ({ value, done }) => {
        expect(value).toBeUndefined()
        expect(done).toBe(true)
    })
})

You can return from your test function to tell redux-saga-jest to send data to generator, terminate it, or signal an error, using special functions next, cancel and error respectively. These functions works much like redux-saga effects, returning an object that tells redux-saga-jest what to do next, rather than resuming execution of generator immediately.

import runSaga, { next } from 'redux-saga-jest'
 
describe('simpleGenerator', () => {
    const { it, expect } = runSaga(simpleGenerator())
 
    it('should yield 1', ({ value }) => {
        expect(value).toBe(1)
        return next('foo')
    })
 
    it('then should yield "foo"', ({ value }) => {
        expect(value).toBe('foo')
    })
 
    it('then should finish', ({ value, done }) => {
        expect(value).toBeUndefined()
        expect(done).toBe(true)
    })
})

Alternatively, use equivalent methods of expect. This will resume the generator immediately and allow you to assert yielded values using method chaining.

import runSaga from 'redux-saga-jest'
 
describe('simpleGenerator', () => {
    const { it, expect } = runSaga(simpleGenerator())
 
    it('should yield 1, then yield "bar", then finish', ({ value }) => {
        expect(value).toBe(1)
        expect.next('bar').value().toBe('bar')
        expect.next().done().toBe(true)
    })
})

For the most part testing sagas is no different from testings plain generators.

redux-saga effects are plain objects, so it's a common practice to test sagas using toEqual, but it's a little verbose and requires importing redux-saga effects in your tests. redux-saga-jest makes it more concise using custom matchers.

Consider the following saga:

import { put, take } from 'redux-saga/effects'
 
function* simpleSaga() {
    yield put({ type: 'FOO', payload: 1})
    const payload = yield take('BAR')
    yield put({ type: 'BAZ', payload })
}

You can test it like this:

import runSaga, { next } from 'redux-saga-jest'
import simpleSaga from './simpleSaga'
 
describe('simpleSaga', () => {
    const { it, expect } = runSaga(simpleSaga())
 
    it('should put an action "FOO" with payload 1', ({ value }) => {
        expect(value).put({ type: 'FOO', payload: 1 })
    })
 
    it('should take an action "BAR"', ({ value }) => {
        expect(value).take('BAR')
        return next(5)
    })
 
    it('should put an action "BAZ" with payload 5', ({ value }) => {
        expect(value).put({ type: 'BAZ', payload: 5 })
    })
 
    it('then should finish', ({ value, done }) => {
        expect(value).toBeUndefined()
        expect(done).toBe(true)
    })
})

License

Licensed under the MIT License.