Of course there is no validator which will check for bugs 🙂
But you can use php -l on each script in turn to determine if there are any compile errors. A simple shell script (with "find" for example) can run this on all the .php files in your project. I use this.
As far as testing is concerned, you can write Javascript (client-side) test cases using "Selenium". You can do server-side unit testing of PHP components using PHPUnit. Both of these may be useful but will require you to write more code.
Mark