commerce-8.x-2.8/tests/modules/commerce_test/commerce_test.module

<?php

/**
 * @file
 * Test module for Commerce.
 */

/**
 * Implements hook_theme().
 */
function commerce_test_theme($existing, $type, $theme, $path) {
  return [
    'render_entity' => [
      'template' => 'commerce-test-entity-render',
      'variables' => [
        'entity' => NULL,
      ],
    ],
  ];
}