Intermittent build failure in NamespacesWfsTest

When building locally, NamespacesWfsTest often fails:

There seems to be state sharing between StationsMockData instances via the static final (i.e. statically initialised) TEST_ROOT_DIRECTORY, and all instances attempt to remove it in tearDown. Fixing this by making it an instance variable did not resolve the failure. There is a similar pattern in NamespacesWfsTest itself but I do not see how this could have multiple instances (final class); I am not sure why this fixture creates two directories. can you see what is going wrong? I wonder if there is some interaction with the one-time setup infrastructure of GeoServerSystemTestSupport (or rather, its shutdown phase)?