I think this used to work, but I suspect that python -mspin test now runs in a new process so that the debugger/lldb doesn't attach to you.

I am not sure that this can be changed easily, FWIW, python lldb -c ..., etc. all work fine (I just like to run a test that fails if it does).

EDIT: This is not new in 0.13, if it changed (I think it did), it changed a while ago.