ReactJS : setup ava for testing react components

31 May 2017

Ava.js is a futuristic test runner, which runs your tests concurrently. This will force you to write tests without depending on a global state or state of other test cases.

Installation

Let’s start with installing ava globally.

npm i -g ava

Once the installation finishes, add ava to our project.

ava --init

Babel config

Since our project already have babel config, we want ava to use the same babel setup to transpile the test code. For this we need to use specia keyword inherit in ava’s babel config.

// package.json

{
  "ava": {
    "babel": "inherit"
  }
}

Adding mocked browser envionment

Unlike other libraries React need browser enviornment for ReactDOM.render and simulate events. We will use browser-env to add mocked browser envionment. browser-env will add variables like window, document etc to the global namespace.

Install the browser-env using

npm i --save-dev browser-env

and add a helper file to load the needed browser global variables.

// tests/helpers/browser-env.js
import browserEnv from 'browser-env';
browserEnv(['window', 'document']);

By default, browserEnv() add all global browser variables to global scope, which not a good idea. browserEnv(['window', 'document']) will expose the needed ones. Since our tests/helpers/browser-env.js doesn’t get transpiled by ava, we need to use babel-register to transpile this on the fly.

npm i --save-dev babel-register

Now we need to specify babel-register & browser-env helper we wrote in ava’s register config to load before the tests.

// package.json

{
  "ava": {
    "babel": "inherit",
    "register": [
      "babel-register",
      "./test/helpers/browser-env.js"
    ]
  } 
}

Ignoring the CSS and Images

Now if we try to run tests for the components which import any css or images, the nodejs will throw an error since they are not valid JavaScript. We can fix this issue by using ignore-styles.

npm i --save-dev ignore-styles

Now we can load this in ava’s register hook.

// package.json

{
  "ava": {
    "babel": "inherit",
    "register": [
      "babel-register",
      "./test/helpers/browser-env.js",
      "ignore-styles"
    ]
  } 
}

Now we are ready to our first test case.

First unit test

Now lets write our first test case

import test from 'ava';

import React from 'react';
import { shallow } from 'enzyme';

import HelloWorld from '../src/HelloWorld';

test('it renders', (t) => {
  const wrapper = shallow(<HelloWorld title="Title" desc="desc"/>);
  t.true(wrapper.hasClass('hello-world'));
})

Now when we run the command ava,

Snapshot testing

Snapshot testing is introduced with jest, to compare and make sure UI didn’t changed unexpectedly. Ava supports snapshot testing using snapshot assetion method.

import test from 'ava';
import render from 'react-test-renderer';

import HelloWorld from '../src/HelloWorld';

test('HelloWorld snapshot', t => {
  const tree = render.create(
    <HelloWorld title="Title" desc="desc"/>
  ).toJSON();
  t.snapshot(tree);
});

This will create snapshot in __snapshots__ folder similar to jest. All the snapshots should be added to source control along with the code. Use -u option to update the snapshots for the latest changes.

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