react-test-context-setup

Low-impact test pattern for setup of react context and provider

Problem

React Context API provides a low-friction method for managing state change without depending on large-overhead libraries such as redux. Testing components which use context is a well-understood problem but isolating the context and provider setup code for testing can be tricky.

Example

Below is the code for setting up a basic context to hold a counter (context.js).

import React, { useReducer } from 'react';
import reducer from './reducer';

const initialState = {
    count: 0
}

const CounterContext = React.createContext(initialState);

const CounterProvider = ({ children }) => {
    const [state, dispatch] = useReducer(reducer, initialState);

    return (
        <CounterContext.Provider value={{ state, dispatch }}>
            { children }
        </CounterContext.Provider>
    );
}

export {
    CounterContext,
    CounterProvider
}

Installation

npm install --save-dev react-test-context-setup

Usage

import React from 'react';
import { render, cleanup } from '@testing-library/react';
import { CounterContext, CounterProvider } from './context';
import ContextTestComponent from 'react-test-context-setup';

afterEach(cleanup);

const renderWithContext = () => {
    return render(
        <CounterProvider>
            <ContextTestComponent
                Context={CounterContext} />
        </CounterProvider>
    );
}

it('initialises count to 0', () => {
    const { getByTestId } = renderWithContext();
    expect(getByTestId('count').textContent).toEqual('0');
});

Explanation

The component ContextTestComponent renders all state from a given context by iterating through the keys of the state object and creating a <div /> where the data-testid is set to the key and the content is set to the value.

For example the following state:

{
    "count": 0,
    "someOtherProperty": "testdata"
}

would be rendered as:

<div>
    <div data-testid="count">0</div>
    <div data-testid="someOtherProperty">testdata</div>
</div>