A simple pre-commit hook to generate a screenshot and diff it with previous screenshot using Headless Chrome and reading URL from a docker-compose.yml file. Don't forget to run chmod a+w on the pre-commit file.

pre-commit

#!/usr/local/bin/php

<?php
/**
 * Just a quick script for Headless Chrome testing
 */

if (!is_dir('tests-visual')) {
  mkdir('tests-visual', 0777);
}

// Rename older screenshot to screenshot-old
if (is_file('tests-visual/screenshot.png')) {
  rename('tests-visual/screenshot.png', 'tests-visual/screenshot-old.png');
}

// Get URL to test
$pattern = '/hostname: &hostname ([^ ]+)/';
preg_match($pattern, file_get_contents('docker-compose.yml'), $matches);
if (isset($matches[1])) {
  // We can now test our app
  $url = trim($matches[1]);

  // Generate screenshot of frontpage
  exec(sprintf('/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome --headless --disable-gpu --screenshot --window-size=1920,1080 http://%s', $url));

  // Move screenshot.png to tests-visual/ directory
  if (is_file('screenshot.png')) {
    rename('screenshot.png', 'tests-visual/screenshot.png');
  }

  // Lets diff our screenshot and open that too
  if (is_file('tests-visual/screenshot-old.png')) {
    exec('compare tests-visual/screenshot-old.png tests-visual/screenshot.png tests-visual/diff.png');

    exec('open tests-visual/diff.png');
  }
}