We will use the example from Recipe 1, Code reuse with functions and macros and keep the C++ sources unchanged and the file tree essentially the same:
.├── cmake│ └── testing.cmake├── CMakeLists.txt├── src│ ├── CMakeLists.txt│ ├── main.cpp│ ├── sum_integers.cpp│ └── sum_integers.hpp
└── tests ├── catch.hpp ├── CMakeLists.txt └── test.cpp