A project I'm working on interacts heavily with Subversion, using svnkit.
Are there any examples on running a mock in-memory svn instance, to help facilitate testing etc?
It's quite straightforward to create a temporary SVN repository on the filesystem to use during the test which you can delete immediately at the end of the test. You would use file:// protocol to access it.
Why don't you just create a simple SVN repository with mock data ? It's just a few commands.