Correct resource paths.
ICrystal extends IAtomContainer... so the second condition was never being checked. A left over gotcha from the removal of IMolecule.
Mutability makes these classes so confusing but the test expects a different chem model for each frame. Also if we delegate the 'list' end element an extra empty chem model is added. So we don't delegate this any more.
Silly test but now resolved - when given a null molecule a null collection is returned.
Test was failing because the test order is not guaranteed. This now works but tests depending on other tests are not good tests.