Include Google Test into a CMake project as external project

googletest.cmake

include(${CMAKE_ROOT}/Modules/ExternalProject.cmake)
ExternalProject_Add(googletest
    GIT_REPOSITORY "https://github.com/google/googletest.git"
    GIT_TAG "master"
    UPDATE_COMMAND ""
    INSTALL_COMMAND "")

SET(GTEST_INCLUDE_DIR ${CMAKE_CURRENT_BINARY_DIR}/googletest-prefix/src/googletest/googletest/include)
SET(GTEST_LIB_DIR ${CMAKE_CURRENT_BINARY_DIR}/googletest-prefix/src/googletest-build/googlemock/gtest)

# Work around for 'non-existent' directory issue/bug
file(MAKE_DIRECTORY ${GTEST_INCLUDE_DIR})

add_library(gtest STATIC IMPORTED)
set_target_properties(gtest PROPERTIES IMPORTED_LOCATION ${GTEST_LIB_DIR}/libgtest.a)
set_target_properties(gtest PROPERTIES INTERFACE_INCLUDE_DIRECTORIES ${GTEST_INCLUDE_DIR})

add_library(gtest_main STATIC IMPORTED)
set_target_properties(gtest_main PROPERTIES IMPORTED_LOCATION ${GTEST_LIB_DIR}/libgtest_main.a)