Fail tests if pages are not cacheable when they should be

ExpectsCacheableResponseTrait.php

<?php

declare(strict_types=1);

namespace Drupal\Tests\my_profile\Traits;

use Behat\Mink\Exception\UnsupportedDriverActionException;
use Drupal\Core\Url;

/**
 * Fails tests if pages are not cacheable when they should be.
 */
trait ExpectsCacheableResponseTrait {

  /**
   * List of dynamic paths that are not cacheable..
   *
   * @var string[]
   */
  private array $dynamicPaths = [
    '/user/login',
    '/big_pipe/no-js',
    '/batch',
  ];

  /**
   * Option to pass to drupalGet to allow uncacheable responses.
   *
   * @todo use a constant in PHP 8.2
   * @see https://php.watch/versions/8.2/constants-in-traits
   */
  private string $uncacheableResponseOption = '_expect_uncacheable_response';

  /**
   * Retrieves a Drupal path without checking cacheability.
   */
  protected function drupalGetUncacheablePage(string|Url $path, array $options = [], array $headers = []): string {
    return $this->drupalGet($path, [$this->uncacheableResponseOption => TRUE] + $options, $headers);
  }

  /**
   * Detects un-cacheable responses and fails if that is not allowed.
   */
  private function detectUncacheableResponse(string|Url $path, array $options = []): void {
    if (($options[$this->uncacheableResponseOption] ?? FALSE)) {
      return;
    }

    if ($this->isDynamicPath($path)) {
      return;
    }

    try {
      if ($this->getSession()->getResponseHeader('X-Drupal-Dynamic-Cache') === 'UNCACHEABLE') {
        $this->fail(sprintf('Found an un-cacheable response at path: %s. If your test visits dynamic pages (cache-lifetime of zero) use ::drupalGetUncacheablePage method instead.', $this->buildUrl($path, $options)));
      }
    }
    catch (UnsupportedDriverActionException $e) {
      // Javascript tests don't support reading response headers.
    }
  }

  /**
   * Determines if the current path is uncacheable.
   */
  private function isDynamicPath(string|Url $path): bool {
    $currentPath = $path instanceof Url ? $path->toString() : $path;
    $currentUrl = $this->getSession()->getCurrentUrl();
    foreach ($this->dynamicPaths as $dynamicPath) {
      if (str_contains($currentUrl, $dynamicPath)) {
        return TRUE;
      }
      if (str_contains($currentPath, $dynamicPath)) {
        return TRUE;
      }
    }
    return FALSE;
  }

}

Usage:

/**
 * {@inheritdoc}
 */
protected function drupalGet($path, array $options = [], array $headers = []): string {
  $content = parent::drupalGet($path, $options, $headers);
  $this->detectUncacheableResponse($path, $options);
  return $content;
}