Introduce four CMake options to enable/disabled test variants or test frameworks

By default all four test variants (Catch2 vs. GTest and Approval vs. Unit) are enabled.

cpp/test/CMakeLists.txt

@@ -1,29 +1,35 @@
 include(FetchContent)
 
-FetchContent_Declare(
-  googletest
-  GIT_REPOSITORY https://github.com/google/googletest.git
-  GIT_TAG v1.16.0
-  GIT_SHALLOW TRUE
-)
+if (BUILD_APPROVAL_TESTS_WITH_GTEST OR BUILD_UNIT_TESTS_WITH_GTEST)
+  FetchContent_Declare(
+    googletest
+    GIT_REPOSITORY https://github.com/google/googletest.git
+    GIT_TAG v1.16.0
+    GIT_SHALLOW TRUE
+  )
+  FetchContent_MakeAvailable(googletest)
+endif()
 
-FetchContent_Declare(
-  catch2 
-  GIT_REPOSITORY https://github.com/catchorg/Catch2.git
-  GIT_TAG v3.8.0
-  GIT_SHALLOW TRUE
-)
+if (BUILD_APPROVAL_TESTS_WITH_CATCH2 OR BUILD_UNIT_TESTS_WITH_CATCH2)
+  FetchContent_Declare(
+    catch2 
+    GIT_REPOSITORY https://github.com/catchorg/Catch2.git
+    GIT_TAG v3.8.0
+    GIT_SHALLOW TRUE
+  )
+  FetchContent_MakeAvailable(catch2)
+endif()
 
-FetchContent_MakeAvailable(googletest catch2)
+if (BUILD_APPROVAL_TESTS_WITH_GTEST OR BUILD_UNIT_TESTS_WITH_GTEST)
+  # Force Google Test to link the C/C++ runtimes dynamically
+  set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
 
-# Force Google Test to link the C/C++ runtimes dynamically
-set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
+  # Disable building GMock
+  set(BUILD_GMOCK OFF CACHE BOOL "" FORCE)
 
-# Disable building GMock
-set(BUILD_GMOCK OFF CACHE BOOL "" FORCE)
-
-# Do not install GTest 
-set(INSTALL_GTEST OFF CACHE BOOL "" FORCE)
+  # Do not install GTest 
+  set(INSTALL_GTEST OFF CACHE BOOL "" FORCE)
+endif()
 
 add_subdirectory(cpp_catch2_approvaltest)
 add_subdirectory(cpp_catch2_unittest)