Example of running Pa11y in parallel

pa11y-queue.js

// Example of running Pa11y in parallel. Now that I found
// this I realise it should definitely be in the examples
// in the repo!
//
// You'll need to install `async` and `pa11y`, probs in a
// package.json. This isn't perfect, might need some
// tweaking. Also runs in Node.js 4+ because I'm far too
// used to typing `const` and arrow functions now.

'use strict';

const createQueue = require('async').queue;
const pa11y = require('pa11y');

// Change the concurrency here to run more tests in parallel
const concurrency = 2;
const urls = [
    'http://www.google.com/',
    'http://www.twitter.com/',
    'http://www.github.com/'
];

// Create a Pa11y test runner
const pa11yTest = pa11y({
    // your default options for all URLs
});

// Create our queue
const queue = createQueue(processUrl, concurrency);
queue.drain = queueDrained;
queue.push(urls); // you could also add them individually

// Process a URL that was passed into the queue
function processUrl (url, done) {
    pa11yTest.run(url, (error, results) => {

        // FYI ignoring errors for now, you might want to log these somewhere

        if (!error) {
            const errorCount = results.filter(result => result.type === 'error').length;
            console.log(`Finished testing ${url}: ${errorCount} errors`);
            // ...or something more interesting
        }

        done();
    });
}

// Called when everything's finished
function queueDrained () {
    console.log('All done!');
}

@rowanmanning Hey nicely done!
What's the maximum concurrency do you think pa11y can handle?