You can install something as simple as a cron job to check for changes every minute or so.
However, in my experience, I found it more flexible to create a continuous integration / build server, such as TeamCity or Hudson, with a task that checks the svn repository every minute or so for updates. If there are updates, you can "deploy" them to the testing directory. The advantage of this route is that you can automate additional tasks, such as restarting the web server and / or running unit tests, as well as only updating upon successful completion, etc.
In addition, it is not necessary that the subversion server resides on the same server as your environment, which needs to be updated.
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