TESTING

Since this project's main purpose is to modify and keep in a consistent state
on-disk structures which are, by their nature, difficult to replace, testing is
very important, especially of the pad and related classes.

All the classes that are not simple containers make use of object invariants to
ensure their state is consistent. These invariants are enforced with a metaclass
that calls the class's _checkInvariant method before and after every public
method call and after construction. These invariants range from simple and cheap
to somewhat expensive checks, but none should have a serious impact on
performance, so they are enabled at runtime as well.

In addition to the invariants, all modules have unittests. These can easily be
run with "nosetests" in the top directory and should be fairly quick. (Nose
should not be required, but I find it very convenient as a test runner though
I do not make use of it as an import at the moment). Invariants themselves are
not individually tested for failure since there is no way to violate an
invariant in a non-buggy class without messing with its internals and I prefer
to keep my unit tests implementation agnostic.

The disk-based pad also needs to ensure that interruptions at any time do not
corrupt the structure -- we want pad operations to ideally be atomic or,
failing that, at least fallback to a known good state, even if the crypt
operation also occurs. This is tested with a combination of unit and functional
tests.

The goal of this project is to maintain at all times 100% line coverage for
unit tests.