Sphinx-locking-test is a project mainly written in RUBY and JAVASCRIPT, it's free.
Testing for sphinx delta index locks
Run rake locking in two seperate terminals, you should see
FATAL: failed to lock /Users/adamholt/code/ey/sphinx-locking-test/db/sphinx/development/user_delta.tmp.spl: Resource temporarily unavailable, will not index. Try --rotate option.occasionally in output for both terminals, when one has a lock and the other tries to update the delta.