MI async status output

Hi,

I'm writing unit tests for my MI parser and was trying to get
GDB to output some out of band, async records of type:
status-async-output.

This type of output normally starts with a + according to the manual.

The manual has a special note that says:
status-async-output contains on-going status information about the
progress of a slow operation. It can be discarded. All status output is
prefixed by ‘+’. 

I built gdb from git/master and ran the mi test suite and looked
at the gdb.log file that was created. Unless I'm missing it, I don't see
this type of output anywhere.

Does this mean that GDB doesn't test this functionality?
Does anyone have a simple recipe for getting GDB to output some
async status output?

Thanks,
Bob Rossi