This directory contains code that is invoked only when running with
self-tests enabled. This self-test code is similar to unit tests, but is
run in the context of a full model run because it covers code that is
difficult to get into a unit test harness. As such, the tests here may
be viewed more as integration tests than unit tests. An example is tests
that cover the PIO interface, since these require building and
initializing the PIO system (which is difficult to do in our unit
testing framework).