postoffice-1.0.x-dev/extensions/postoffice_inline_styles/postoffice_inline_styles.install

<?php

/**
 * @file
 * Install, update and uninstall functions for Postoffice Inline Styles module.
 */

/**
 * Implements hook_requirements().
 */
function postoffice_inline_styles_requirements($phase) {
  $requirements = [];

  if (!class_exists('\TijsVerkoyen\CssToInlineStyles\CssToInlineStyles')) {
    $requirements['postoffice_inline_styles_status'] = [
      'title' => t('Postoffice Inline Styles'),
      'description' => t('Composer dependency missing: tijsverkoyen/css-to-inline-styles.'),
      'severity' => REQUIREMENT_ERROR,
    ];
  }

  return $requirements;
}