Fatal error when activating my custom wordpress plugin

Question

What I conclude form your comments is pethouseuk-functionality.php

include 'AlterTableComments.php';

use PethouseukFunctionality\AlterTable;

$a="PethouseukFunctionality\AlterTable\test";
$a();  // function call

$b = 'PethouseukFunctionality\AlterTable\AlterTableComments';
$c = new $b; // new object

$c->yourfunction('test'); // Method call

Another file AlterTableComments.php

<?php

namespace PethouseukFunctionality\AlterTable;

interface AlterTableInterface{

    function yourfunction($param);

}

class AlterTableComments implements AlterTableInterface{
    function yourfunction($param){
        var_dump($param);
    }
}

function test(){
    echo 'this is test ';
}

Result:
this is test string(4) “test”