Assert HTML validity with PHPUnit.

BaseTestCase.php

<?php

use PHPUnit_Framework_Exception;
use PHPUnit_Framework_TestCase;
use SimpleXMLElement;

class BaseTestCase extends PHPUnit_Framework_TestCase
{
	/**
	 * Show as much error information as possible
	 */
	protected $traceError = TRUE;

	/**
	 * Assert that the given HTML validates
	 *
	 * Modified <http://git.io/BNxJcA>. Read the terms of service for
	 * Validator.nu at <http://about.validator.nu/#tos>.
	 *
	 * @param string $html The HTML to validate
	 */
	public function assertValidHtml($html)
	{
		// cURL
		$curl = curl_init();
		curl_setopt_array($curl, [
			CURLOPT_URL            => 'http://html5.validator.nu/',
			CURLOPT_RETURNTRANSFER => TRUE,
			CURLOPT_POST           => TRUE,
			CURLOPT_POSTFIELDS     => [
				'out'     => 'xml',
				'content' => $html,
			],
		]);
		$response = curl_exec($curl);
		if (!$response) {
			$this->markTestIncomplete('Issues checking HTML validity.');
		}
		curl_close($curl);

		// Fail if errors
		$xml = new SimpleXMLElement($response);
		$nonDocumentErrors = $xml->{'non-document-error'};
		$errors = $xml->error;
		if (count($nonDocumentErrors) > 0) {
			// Indeterminate
			$this->markTestIncomplete();
		} elseif (count($errors) > 0) {
			// Invalid
			$this->fail("HTML output did not validate.");
		}

		// Valid
		$this->assertTrue(TRUE);
	}
}