I think the aspect of tidying up here is no different from what folks using any of the builds should expect – to elaborate, lets say you execute this command:
(or 'maven test', or 'ant'), you'll find a bunch of artifacts created in the target directory. These persist until you clean the build, so in the above case a:
will do the trick. The serialization files follow a similar pattern, they can be cleaned using the corresponding clean command.
A useful advantage of using File I/O is that the artifacts can be introspected once you run the tests and you can observe how certain changes to the datamodel or history affect size on disk etc.
You are right that this can be replaced by using ByteArray I/O instead, but at this point its unclear we should (its much harder to introspect serializations or track serialization timelines that way).
Resolving as Won't Fix.