AMP eligible post type test.

amp-eligible-post-type-test.php

<?php
/**
 * Plugin Name: AMP eligible post type test.
 * Description: Plugin to test eligible post types for AMP
 * Version: 0.1
 *
 * @wordpress-plugin
 * @author Dhaval Parekh
 */

add_action( 'init', function () {

	register_post_type(
		'book',
		[
			'label'              => 'Book',
			'publicly_queryable' => true,
		]
	);
	register_post_type(
		'car',
		[
			'label'              => 'Car',
			'public'             => false,
			'publicly_queryable' => true,
		]
	);
	register_post_type(
		'secret',
		[
			'label'              => 'Secret',
			'publicly_queryable' => false,
		]
	);
	register_post_type(
		'secret_book',
		[
			'label'              => 'Secret book',
			'public'             => true,
			'publicly_queryable' => false,
		]
	);
	register_post_type(
		'secret_car',
		[
			'label'              => 'Secret Car',
			'public'             => false,
			'publicly_queryable' => true,
		]
	);
} );

add_filter( 'is_post_type_viewable', function ( $is_viewable, $post_type ) {

	if ( 'secret_car' === $post_type->name ) {
		return false;
	}

	return $is_viewable;
}, 10, 2 );