Test 01

<?php
/*
    Plugin Name: TEST PLUGIN
    Description: TEST
    Author: Krzysztof Kubiak
    Version: 1.0
*/
add_action('admin_init', 'Test_01_settings_init' );
function Test_01_settings_init(){
    register_setting( 'Test_01_settings_filed', 'Test_01_options', 'Test_01_validate' );
}
add_action('init', 'T01_init_method');
function T01_init_method() {
    wp_enqueue_script('jquery');
    wp_register_style( 'Test_01-style', plugins_url('css/style.css', __FILE__) );
}
add_action('admin_menu', 'Test_01_menu_page');
function Test_01_menu_page(){
    add_menu_page( 'Test_01', 'Test_01', 'manage_options', 'T01_menu_page', 'T01_add_page' );
    echo my_test();
}
function my_test(){
    echo 'Function test';
}
function T01_add_page() {
    echo 'TEST_01_plugin';
}

function Test_01_validate($input) {
}

class Test_01_shortcode_selector extends WP_Widget {
    function __construct() {
        parent::__construct(
            'T01_widget', // Base ID
            __('T01_WIDGET', 'text_domain'), // Name
            array( 'description' => __( 'TEST WIDGET', 'text_domain' ), ) // Args
        );
    }
    public function widget( $args, $instance ) {
        wp_enqueue_script( 'jquery' );
        echo 'Test_01:<br>';

        function test_callback() {
            $whatever = 8;
            echo $whatever;
            die();
        }
        add_action( 'wp_ajax_nopriv_testaction', 'test_callback' );
        add_action( 'wp_ajax_testaction', 'test_callback' );
?>
        <script type="text/javascript" >
            jQuery(document).ready(function($) {
                var data = {
                    action: 'testaction'
                };

                $.post(ajaxurl, data, function(ret2) {
                    console.log('Got this from the server: ' + ret2);
                });
            });
        </script> <?php
    }
    public function form( $instance ) {
        echo 'Widget';
    }
    public function update( $new_instance, $old_instance ) {
        $instance = array();
    }
}
add_action('widgets_init', 'register_Test_01_shortcode_selector');
function register_Test_01_shortcode_selector() {
    register_widget( 'Test_01_shortcode_selector' );
}
?>