[React Testing] Create a Custom Render Function to Simplify Tests of Redux Components

It’s very common for our components to use state from the redux store (or to be refactored to use it eventually). Having to change our tests every time we do this would be frustrating. Let’s see how we can write a render method we could use to not worry about that implementation detail when it’s irrelevant for our tests. This could be combined with the custom render method for the router to be a single render method that supports all providers our components need.

Component:

import React from 'react'
import { useSelector } from 'react-redux'
import { rootSelector } from '../reducers/beerReducer'
import BeerList from './BeerList'

export default function Beers() {
  const { data, status, messages } = useSelector(rootSelector)

  return (
    <>
      {status === 'idle' && (
        <div className="App-content">
          <p>Get started by searching beers or get random ones</p>
        </div>
      )}
      {status === 'pending' && (
        <div className="App-content">
          <p>Loading Beers!...</p>
        </div>
      )}
      {status === 'success' && (
        <div className="App-content">
          <BeerList beers={data} />
        </div>
      )}
      {status === 'failure' && (
        <div className="App-messages">
          <p>Oops! {messages[0].text}</p>
        </div>
      )}
    </>
  )
}

Reducer:

import {
  SET_STATUS,
  FETCH_FULFILLED,
  FETCH_FAILED,
  RESET,
} from '../actions/beerActions'
import { createReducer } from '../utils/utils'
import { lensProp, set, view, compose, prop } from 'ramda'

const initialState = {
  data: [],
  status: 'idle', // 'idle' || 'pending' || 'success' || 'failure'
  messages: [],
}

const rootLens = lensProp('beers')
const statusLens = lensProp('status')
const dataLens = lensProp('data')
const messagesLens = lensProp('messages')

const setStatus = set(statusLens)
const setData = set(dataLens)
const setMessages = set(messagesLens)

const viewRoot = (lens) => view(compose(rootLens, lens))
const viewStatus = viewRoot(statusLens)
const viewData = viewRoot(dataLens)
const viewMessages = viewRoot(messagesLens)

const fetchFulfilled = (data, state) => {
  return compose(setData(data), setStatus('success'), setMessages([]))(state)
}

const reset = (_, state) => compose(setStatus('idle'), setMessages([]))(state)

const fetchFailed = (messages, state) => {
  return compose(
    setStatus('failure'),
    setMessages([{ type: 'error', text: messages }]),
  )(state)
}

const reducers = {
  [RESET]: reset,
  [SET_STATUS]: setStatus,
  [FETCH_FULFILLED]: fetchFulfilled,
  [FETCH_FAILED]: fetchFailed,
}

export const beersReducers = (state = initialState, action) =>
  createReducer(reducers, state, action)

export const rootSelector = prop('beers')
export const beersSelector = viewData
export const messagesSelector = viewMessages
export const statusSelector = viewStatus

export const createReducer = (reducers, state, { type, payload }) =>
  propOr(() => state, type, reducers)(payload, state)

Test:

import React, { Children } from 'react'
import { render, queryByTestId, queryAllByTestId } from '@testing-library/react'
import { Provider } from 'react-redux'
import { createStore } from 'redux'

import Beers from '../Beers'
import { beersReducers } from '../../reducers/beerReducer'
import { configureStore } from '../../configureStore'

function renderReducer(ui, options = {}) {
  const store =
    options.store || createStore(options.reducer, options.initialState)
  function Wrapper({ children }) {
    return <Provider store={store}>{children}</Provider>
  }
  return {
    ...render(ui, { wrapper: Wrapper, ...options }),
    store,
  }
}

test('can render redux with custom initial state', () => {
  const { getByText } = renderReducer(<Beers />, {
    reducer: beersReducers,
    initialState: {
      beers: {
        status: 'pending',
        data: [],
        messages: [],
      },
    },
  })

  expect(getByText(/loading Beers!.../i)).toBeTruthy()
})

test('can render redux with custom initial state', () => {
  const { queryByTestId, queryAllByTestId } = renderReducer(<Beers />, {
    reducer: beersReducers,
    initialState: {
      beers: {
        status: 'success',
        data: [
          {
            id: 1,
            name: 'some beer',
            volume: { unit: 1 },
            abv: '',
          },
        ],
        messages: [],
      },
    },
  })

  expect(queryByTestId('beerList')).toBeTruthy()
  expect(queryAllByTestId('beerItem').length).toEqual(1)
})

test('can render initial status with a hint for search', () => {
  const { getByText, debug } = renderReducer(<Beers />, {
    store: configureStore(),
  })
  expect(getByText(/get started by searching beers/i)).toBeTruthy()
})