[CMake] Do not build vtkdiff or gtest when BUILD_TESTING=OFF

CMakeLists.txt

@@ -272,7 +272,7 @@ include_directories(
     ${CMAKE_CURRENT_SOURCE_DIR}/ThirdParty/spdlog/include)
 
 # vtkdiff
-if(EXISTS ${PROJECT_SOURCE_DIR}/ThirdParty/vtkdiff/CMakeLists.txt)
+if(EXISTS ${PROJECT_SOURCE_DIR}/ThirdParty/vtkdiff/CMakeLists.txt AND BUILD_TESTING)
     add_subdirectory(ThirdParty/vtkdiff)
     install(PROGRAMS $<TARGET_FILE:vtkdiff> DESTINATION bin COMPONENT ogs_extras)
 endif()

ThirdParty/CMakeLists.txt

 add_subdirectory(spdlog)
 set(DISABLE_WARNINGS_TARGETS spdlog)
 
-set(gtest_force_shared_crt ON CACHE INTERNAL "") # Use dynamic MSVC runtime
-set(INSTALL_GTEST OFF CACHE INTERNAL "")
-add_subdirectory(googletest)
+if(BUILD_TESTING)
+    set(gtest_force_shared_crt ON CACHE INTERNAL "") # Use dynamic MSVC runtime
+    set(INSTALL_GTEST OFF CACHE INTERNAL "")
+    add_subdirectory(googletest)
+endif()
 
 # This is a workaround for Travis builds.
 option(OGS_USE_OPTIONAL_SUBMODULES "Option for enabling optional submodules" OFF)

scripts/cmake/SubmoduleSetup.cmake

@@ -18,9 +18,11 @@ set(REQUIRED_SUBMODULES
     ThirdParty/spdlog
     ThirdParty/tclap
     ThirdParty/tetgen
-    ThirdParty/vtkdiff
     ${OGS_ADDITIONAL_SUBMODULES_TO_CHECKOUT}
 )
+if(BUILD_TESTING)
+    list(APPEND REQUIRED_SUBMODULES ThirdParty/vtkdiff)
+endif()
 if(OGS_BUILD_UTILS)
     # Required by the partmesh tool, which is build with utils only.
     list(APPEND REQUIRED_SUBMODULES ThirdParty/metis)

scripts/cmake/test/OgsTest.cmake

 function (OgsTest)
-    if(NOT OGS_BUILD_CLI)
+    if(NOT OGS_BUILD_CLI OR NOT BUILD_TESTING)
         return()
     endif()
     set(options LARGE)