Custom fields to save multiple values

I’m adding custom meta-box, by means of jquery I can create in it several custom fields with a key “test”. There can be one or several custom fields, but the key is only “test”. I can also delete key values, which are no longer required. The problem is that I can’t save several values of the custom field with the same key. Only the last value is saved in all the fields. Help me, please, to find a decision!

<?php add_action( 'add_meta_boxes', 'add_test_meta_box' );  
    function add_test_meta_box()  
    {  
        add_meta_box( 'test_meta_box', 'TEST PARAM', 'add_test_meta', 'post', 'normal', 'high' );      
    }  

    function add_test_meta( $post )  
    {  
        // Grab our data to fill out the meta boxes (if it's there)  
        $test = get_post_meta( $post->ID, 'test', true ); 

        // Add a nonce field 
        wp_nonce_field( 'save_test_meta', 'test_meta' ); 
        ?> 

        <div id="myfor">
            <p> 
                <label>Param 1 key "test" </label><br >
                <input type="text" name="test" value="<?php echo esc_attr( $test ); ?>"  size="60" /><span>Delete</span>
            </p> 
        </div>

        <input type="button" value="Добавить" id="addnew">

        <?php 
    } 

    add_action( 'save_post', 'test_meta_save' ); 
    function test_meta_save( $id ) 
    { 
        // No auto saves 
        if( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) return;  

        // Check our nonce 
        if( !isset( $_POST['test_meta'] ) || !wp_verify_nonce( $_POST['test_meta'], 'save_test_meta' ) ) return; 

        // make sure the current user can edit the post 
        if( !current_user_can( 'edit_post' ) ) return; 

        // strip all html tags and esc attributes here 
        if( isset( $_POST['test'] ) ) 
            update_post_meta( $id, 'test', esc_attr( strip_tags( $_POST['test'] ) ) );   
    }  

    add_action('admin_head', 'my_add_input');


    function my_add_input() { ?>
      <script>
      // add live metod 
      jQuery.fn.live = function (types, data, fn) {
        jQuery(this.context).on(types,this.selector,data,fn);
        return this;
    };

    // add new input
      (function($){ 
          $(function(){ 

            var num = 2;


            $('#addnew').click(function(){
                $('#myfor').append('<p><label>Param  '+ num +' key "test" </label><br ><input type="text" name="test" value=""  size="60" /> <span>Delete</span></p>');
                num ++;
            });

            $('span').live( 'click' , function(){       
                $(this).parent('p').remove();
            });     

        });  
    })(jQuery)  
      </script>

    <?php } ?>