[bhawks]

Posix file system semantics are very complex. An in memory implementation is likely to have quality gaps that make it sub optimal. If you want fast tests /tmp is likely to be backed by tmpfs in memory. If you are paranoid you can use /dev/shm to be explicit about your desire.

Going this route means you're going to leverage all the well tested Linux VFS code and your tests will execute with higher fidelity.