This directory contains unit tests for engine.  We are using googletest (gtest) currently,
but only in a fairly naive manner.

However, gtest does not play well with libgc, at least I could not get them to work together.
We create our own executable here (or, executables), and have a number of files which avoid the
use of libgc, as well as avoid needing to link in d directory 
(M2mem-replacement, M2-replacement, M2-cpp-replacement).

Run tests (and compiles them) using: make check
  Currently, this also is when the file gtest-includes is compiled (which takes a bit of time)

Currently, the source files (except gtest-include.cpp) are compiled during 'make'

We are experimenting with using catch2 instead of gtest, and also with trying to build the 
unit test executable via cmake.
