And retro-fitting unit tests to existing code isn't much fun. However, it is entertaining for the number of latent bugs it finds! There's always something special about output like:
[----------] 2 tests from Image [ RUN ] Image.Empty Segmentation fault (core dumped)
Noting that the unit test in question creates an unparametrised object and inquires as to it's size. :)
Off to fire up a debugger and find out wtf is going on.