https://coenjacobs.me/2018/05/30/decouple-wordpress-databases-repositories/

example-coupled-meta-class.php

<?php

class MetaChecker {
  public function checkMeta( WP_Post $post ) {
    $value = get_post_meta($post->ID, 'key_of_value_store', true);
    
    // @TODO: Do magic with $value
  }
}

implemented-repository.php

<?php

class MetaChecker {
   /** @var MetaRepository */
   public $metaRepository;

   public function __construct( MetaRepository $metaRepository ) {
      $this->metaRepository = $metaRepository;
   }

   public function checkMeta( WP_Post $post ) {
      $value = $this->metaRepository->getMeta($post, 'key_of_value_store', true);

      // @TODO: Do magic with $value
   }
}

interface-repository.php

<?php

interface MetaRepository {
  public function getMeta( WP_Post $post, $key, $single );
}

class WordPressMetaRepository implements MetaRepository {
  public function getMeta( WP_Post $post, $key, $single ) {
    return get_post_meta($post->ID, $key, $single);
  }
}