[I can't figure out how to accomplish this from `nosetests --help` and googling didn't help either]
I just ran into this issue while implementing unit tests for an asynchronous module based on the Twisted reactor event loop. Once the test starts, it initiates some asynchronous activities and then calls `reactor.run()` which blocks until something in the test calls `reactor.stop()`. Once stopped, subsequent tests in the test suite that need to call `reactor.run()` fail with the `twisted.internet.error.ReactorNotRestartable` exception. Twisted doesn't have the notion of creating additional event loops - there is only one by design, and it can't be restarted once stopped (also by design).
So, the only way that I can run more than one test, is to run each test in process isolation. pytest supports the `--boxed` option that guarantees that each test will run in its own process that won't be reused for any other tests.
I tried nosetests options `--with-isolation` and `--processes`, but they don't help.