An example cmake project to demonstrate relations between cmake targets.
We have libraries for sum, multiplication, factorial, and substraction. The multiplcation library uses the sum library to implement multiplication operation. The factorial library uses the multiplication library to compute the factorial of a given integer. CMake regulates the relations between these libraries without exposing more than their public interfaces. For example, the factorial library doesn't know about the implementation details of the multiplication library. If we change the the multiplication library to simply use multiplication operator rather than utilizing the sum library, the factorial library doesn't need any change at all. Each of these libraries are also tested using GTest. GTest dependency is managed by conan, C/C++ package manager. We have two client applications, app1 and app2. These applications use our highly-modular, reusable, well-tested libraries.
As a summary, we divide each functional component into a library. We define interfaces for these libraries in their header files. As we implement these interfaces, we either write unit tests or alternatively, go for Test Driven Development. We can also start writing applications when the library interfaces reach to a certain level of stabilization. If applications are simple CLI apps, CTest is enough to test their outputs with specified inputs. Otherwise, they may require different integration testing strategies.
Assuming you have cmake and conan installed, run the following commands.
mkdir build
cd build
conan install ..
cmake -DCMAKE_BUILD_TYPE=Debug -DCMAKE_VERBOSE_MAKEFILE=ON ..
cmake --build ..
ctest --verbose
./bin/app1
./bin/app2