A custom post type plugin for WordPress. The plugin will add the custom post type Projects and these posts will also feature a metabox that allows you to toggle whether the post is featured.

custom-posts.php

<?php
/**
 * Plugin Name: Custom Post Types
 * Plugin URI: https://gist.github.com/nosquirrelbones/316a29936e5e7d709665
 * Description: A simple plugin (template) to register custom post types
 * Version: 1.1
 * Author: James Robinson
 * Author URI: http://jmr.codes/
 * License: GPL2
 */

/*
	Copyright 2017 James Robinson

	This program is free software; you can redistribute it and/or modify
	it under the terms of the GNU General Public License, version 2, as
	published by the Free Software Foundation.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program; if not, write to the Free Software
	Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

if ( !defined( 'ABSPATH' ) ) exit;

function jmr_custom_posts() {


	// ************* CLIENTS *************************************** //
	// ** THIS IS A HIDDEN POST TYPE FOR BACKEND USE. ************** //

	$client_labels = array(
		'name'               => __( 'Client', 'post type general name', 'jmr-cpt' ),
		'singular_name'      => __( 'Client', 'post type singular name', 'jmr-cpt' ),
		'menu_name'          => __( 'Clients', 'admin menu', 'jmr-cpt' ),
		'name_admin_bar'     => __( 'Client', 'add new on admin bar', 'jmr-cpt' ),
		'add_new'            => __( 'Add New', 'client', 'jmr-cpt' ),
		'add_new_item'       => __( 'Add New Client', 'jmr-cpt' ),
		'edit_item'          => __( 'Edit Client', 'jmr-cpt' ),
		'new_item'           => __( 'New Client', 'jmr-cpt' ),
		'all_items'          => __( 'All Clients', 'jmr-cpt' ),
		'view_item'          => __( 'View Client', 'jmr-cpt' ),
		'search_items'       => __( 'Search Client', 'jmr-cpt' ),
		'not_found'          => __( 'No clients found', 'jmr-cpt' ),
		'not_found_in_trash' => __( 'No clients found in the Trash', 'jmr-cpt' ),
		'parent_item_colon'  => '',
		'menu_name'          => 'Clients'
	);

	$client_args = array(
		'labels'        => $client_labels,
		'description'   => 'Contains client logos and links',
		'public'        => false,
		'show_ui'		=> true,
		'menu_position' => 5,
		'menu_icon'     => 'dashicons-businessman',
		'supports'      => array( 'title', 'editor', 'excerpt', 'thumbnail' ),
		'rewrite'       => false,
		'has_archive'   => false,
		'hierarchical'  => false
	);

	register_post_type( 'client', $client_args );


	// ************* TESTIMONIAL *************************************** //
	// ** THIS IS A PUBLICLY VISIBLE POST TYPE WITH REWRITES, ETC. ***** //

	$testimonial_labels = array(
		'name'               => __( 'Testimonial', 'post type general name', 'jmr-cpt' ),
		'singular_name'      => __( 'Testimonial', 'post type singular name', 'jmr-cpt' ),
		'add_new'            => __( 'Add New', 'testimonial', 'jmr-cpt' ),
		'add_new_item'       => __( 'Add New Testimonial', 'jmr-cpt' ),
		'edit_item'          => __( 'Edit Testimonial', 'jmr-cpt' ),
		'new_item'           => __( 'New Testimonial', 'jmr-cpt' ),
		'all_items'          => __( 'All Testimonials', 'jmr-cpt' ),
		'view_item'          => __( 'View Testimonials', 'jmr-cpt' ),
		'search_items'       => __( 'Search Portfolio', 'jmr-cpt' ),
		'not_found'          => __( 'No testimonials found','jmr-cpt' ),
		'not_found_in_trash' => __( 'No testimonials found in the Trash', 'jmr-cpt' ),
		'parent_item_colon'  => '',
		'menu_name'          => 'Testimonials'
	);

	$testimonial_args = array(
		'labels'        => $testimonial_labels,
		'description'   => __('Contains testimonials', 'jmr-cpt'),
		'exclude_from_search' => true,
		'public'        => true,
		'show_ui'		=> true,
		'menu_position' => 5,
		'menu_icon'     => 'dashicons-smiley',
		'supports'      => array( 'title', 'editor', 'excerpt' ),
		'rewrite'       => array(
			'slug' => 'testimonial',
			'with_front' => true,
			'feeds' => true,
			'pages' => true
		),
		'has_archive'   => false,
		'show_in_rest' 	=> true
	);

	register_post_type( 'testimonial', $testimonial_args );

}

add_action( 'init', 'jmr_custom_posts' );


// ************* FLUSH URL REWRITE RULES ***************************** //

function rmd_rewrite_flush() {
	rmd_custom_posts();
	flush_rewrite_rules();
}
register_activation_hook( __FILE__, 'jmr_rewrite_flush' );

This code is adapted from in a tutorial in Smashing Magazine by Daniel Pataki