public function dataProviderForFunctionMatrix()
{
$function = function ($x) {
return $x * 2;
};
return [[[[$function, $function]]], [[[$function, $function], [$function, $function], [$function, $function]]], [[[$function, $function, $function], [$function, $function, $function], [$function, $function, $function], [$function, $function, $function]]]];
}