chore(build): only build tests when standalone

Author: fallenoak

CMakeLists.txt

@@ -22,5 +22,9 @@ include(lib/system/cmake/system.cmake)
 
 add_subdirectory(lib)
 add_subdirectory(common)
-add_subdirectory(test)
 add_subdirectory(vendor)
+
+# Only build tests when standalone
+if(CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR)
+    add_subdirectory(test)
+endif()