Comment 8 for bug 666345

E.g.

=== modified file 'testtools/_spinner.py'
--- testtools/_spinner.py 2010-11-30 17:07:56 +0000
+++ testtools/_spinner.py 2010-12-13 20:13:47 +0000
@@ -232,7 +232,6 @@
             # we aren't going to bother.
             junk.append(selectable)
         if IReactorThreads.providedBy(self._reactor):
- self._reactor.suggestThreadPoolSize(0)
             if self._reactor.threadpool is not None:
                 self._reactor._stopThreadPool()
         self._junk.extend(junk)

should fix it.