<?php
/**
 * Get post Lists
 *
 * @throws \InvalidArgumentException If the post type doesn't exists.
 *
 * @param string $postType
 *
 * @return array An array of key value pair where the key is the post name and the value the post title.
 */
function getPostList($postType)
{
    if (! post_type_exists($postType)) {
        throw new \InvalidArgumentException(
            sprintf(esc_html__('Post Type %s does not exists.', 'textdomain'), $postType)
        );
    }

    $list = array();

    // Retrieve the posts.
    $query = new \WP_Query([
        'post_type'      => $postType,
        'posts_per_page' => -1,
        'no_found_rows'  => true,
    ]);

    // Create the list.
    if ($query->have_posts()) {
        foreach ($query->posts as $post) {
            $list[$post->post_name] = $post->post_title;
        }
    }

    return $list;
}