Test running out of disk space

[adamgundry]

We ought to have a test for what happens when the disk is full. This can be modelled as in #58 using tmpfs, but doing so requires root privileges. Perhaps that's okay though.

Are there any other good options? I wondered about creating a mock file handle implementation that simulates disk full behaviour after a certain number of bytes have been written...

[stepcut]

Using tmpfs would make that particular test Linux-only. Obviously that is still better than no test at all. It is certainly the most accurate test since the file system really does run out of space.

I like the idea of a mock file handle implementation. Conveniently we already abstract out the key FHandle, open, and write in FileIO so that we can have different implementations for win32 vs everybody else.

It seems like we would add src-test/win32, src-test/linux, where the FHandle has a quota value we can set dynamically. When the quota is hit we can throw whatever error was actually be thrown?

It would be neat to generalize this for use with other applications, but this would be sufficient for us I think.