usage:
register_tests(SOURCES
                 ${list_of_source_files}
                 "test_src.cc"
                 ${concatenated_string_of_source_files}
               NAMESPACE
                 "test_namespace"
               DEPENDS
                 ${list_of_targets}
               INCLUDES
                 ${list_of_include_directories}
               COMPILE_OPTIONS
                 ${list_of_compile_options})

Function registers tests defined as a list of souce files.  Test defined
by file source_name.cc in the SOURCES list is registered under the name
  test_namespace.source_name

Provided list of dependent targets and include directories are used for
test executables as PRIVATE dependencies during compilation.

Function implicitly adds a dependency on the boost unit test framework
to each generated test executable.