Extract googletest cmake into proper file

Author: xtofl

src/AddGoogleTest.cmake

@@ -0,0 +1,15 @@
+cmake_minimum_required(VERSION 3.11.0)
+
+include(FetchContent)
+FetchContent_Declare(
+  googletest
+  GIT_REPOSITORY https://github.com/google/googletest.git
+  GIT_TAG        release-1.8.0
+)
+FetchContent_MakeAvailable(googletest)
+FetchContent_GetProperties(googletest)
+if(NOT googletest_POPULATED)
+  FetchContent_Populate(googletest)
+  add_subdirectory(${googletest_SOURCE_DIR} ${googletest_BINARY_DIR})
+endif()
+

src/CMakeLists.txt

@@ -3,18 +3,7 @@ cmake_minimum_required(VERSION 3.11.0)
 set(CMAKE_CXX_STANDARD 17)
 project(cpp11training)
 
-include(FetchContent)
-FetchContent_Declare(
-  googletest
-  GIT_REPOSITORY https://github.com/google/googletest.git
-  GIT_TAG        release-1.8.0
-)
-FetchContent_MakeAvailable(googletest)
-FetchContent_GetProperties(googletest)
-if(NOT googletest_POPULATED)
-  FetchContent_Populate(googletest)
-  add_subdirectory(${googletest_SOURCE_DIR} ${googletest_BINARY_DIR})
-endif()
+include(AddGoogleTest.cmake)
 
 project(cpp11training)
 file (GLOB_RECURSE SOURCES "${CMAKE_CURRENT_SOURCE_DIR}/*.cpp")