I know that in a project on which I am working I use Boost.Test in header-only mode and it works fine when using b2 to run tests for the project. I would like to think that if I try to use CMake to run tests for the project using the header-only variant of Boost.Test it will continue to work fine. That's all really.
Peter wrote that he implemented that in https://github.com/boostorg/test/commit/bce2d24c8b32f47f0403766fe4fee3e2e93a... So all you got to do is "link" to `Boost::included_unit_test_framework` and you can use it header-only. "Link" in CMake terms, no actual linking done, only declaring a dependency, and getting the headers into the include path. Although I would have used `header_only` as a suffix instead, but well, naming ;)