Code review comment for lp:~justin-fathomdb/nova/constraint-scheduler

It's easy to miss, but the ConstraintDriverTestCase derives from
_SchedulerBaseTestCase, so inherits basically the same code coverage as the
SimpleScheduler (although the SimpleScheduler supports some 'directed
placement' in a bit of a hacky way, which I don't support in the
ConstraintScheduler) But the ConstraintScheduler (which is never used
unless someone specifically requests it) behaves the same way as the
SimpleScheduler under the basic tests.

In addition, there are unit tests for the constraint solving library.

I believe that's reasonable test coverage. There can always be more tests,
but I think this is a reasonable start for something that is only
user-selectable. As we add use-cases, I'm sure we'll find issues and add
tests, both for bugs, and places where extra behaviour is needed. I did
find a bug when developing the derived directed-location branch, and I
back-ported that fix (which is how I broke the unit tests in the first
place!) That bug was when the min-scores were tied, it didn't fall-back to
consider the secondary criteria. The constraint solving library tests
didn't hit this because they were using randomized data, so were very
unlikely to get ties.

Is that OK?