Task #1587: improve the configurability of regression tests
Unit tests for bonded forces
As part of moving away from tedious testing of forces using regression tests (or as a complement to it) it would be good to have unit tests for bonded forces. They can be built up in part, say one function at a time to have not too much code to check.
Added first tests of bonded force functions.
Tests for bond_angle and dih_angle functions.
Some tests for bondeds, angles and dihedrals.
Part of #2034