When using the php-mock library on PHP 8.4 I'm getting the following warnings when running my tests:

phpmock\spy\Spy::__construct(): Implicitly marking parameter $function as nullable is deprecated, the explicit nullable type must be used instead

phpmock\spy\Invocation::__construct(): Implicitly marking parameter $exception as nullable is deprecated, the explicit nullable type must be used instead

Since explicit nullable parameter support was added in PHP 7.1, I believe a fix for this would require either bumping the minimum version to 7.1 (from 5.6) or removing the explicit declaration of the type.