In this recipe, we will build and test the same source files, main.cpp, sum_integers.cpp, sum_integers.hpp, and test.cpp, as in Chapter 4, Creating and Running Tests, Recipe 3, Defining a unit test and linking against Google Test. We will download all required Google Test sources at configure time using FetchContent or ExternalProject_Add and in this recipe only focus on the fetching of dependencies at configure time, not so much on the actual source code and its unit tests.