Use php namespace inside function

From the manual:

The use keyword must be declared in the outermost scope of a file (the global scope) or inside namespace declarations.

From Scoping rules for importing

The use keyword must be declared in the outermost scope of a file (the global scope) or inside namespace declarations. This is because the importing is done at compile time and not runtime, so it cannot be block scoped

So you should put like this, use should specified at the global level

require('/var/load.php');
use test\Class;

function go(){
    $go = 'ok';
    return $go;
}
echo go();

Check the example 5 in the below manual Please refer to its manual at http://php.net/manual/en/language.namespaces.importing.php