The libdhcp++ API was changed as part of the refactoring.

When linking new tests to old library it fails with:

/libexec/ld-elf.so.1:
/usr/home/jreed/builder/work/BIND10-cppcheck/20120516153001-FreeBSD8-amd64-GCC/build/src/bin/dhcp4/tests/.libs/dhcp4_unittests:
Undefined symbol "_ZN3isc4dhcp6OptionC1ENS1_8UniverseEtRKSt6vectorIhSaIhEE"

This is:
 isc::dhcp::Option::Option(isc::dhcp::Option::Universe, unsigned short,
std::vector<unsigned char, std::allocator<unsigned char> > const&)

See http://bind10.isc.org/wiki/LibraryVersioning for details.