The FetchContent module enables populating content at configure time, via any method supported by the ExternalProject module, and has become a standard part of CMake in its 3.11 version. Whereas ExternalProject_Add() downloads at build time (as seen in Chapter 8, The Superbuild Pattern), the FetchContent module makes content available immediately, such that the main project and the fetched external project (in this case, the Google Test) can be processed when CMake is first invoked, and can be nested using add_subdirectory.
To fetch Google Test sources, we have first declared the external content:
include(FetchContent)FetchContent_Declare( googletest GIT_REPOSITORY https://github.com/google/googletest.git GIT_TAG release-1.8.0 ...
