Use ctest of default BUID_TESTING flag

CMakeLists.txt

@@ -127,7 +127,10 @@ export(EXPORT dune-copasi-targets
 add_library(dune::copasi ALIAS dune-copasi)
 
 # include tests as a sub project
-add_subdirectory(test)
+include(CTest)
+if(BUILD_TESTING)
+  add_subdirectory(test)
+endif()
 
 # add definitions for packaging
 include(SetupDuneCopasiCPack)
\ No newline at end of file

test/CMakeLists.txt

 cmake_minimum_required(VERSION 3.13)
 project(dune-copasi-tests CXX)
 
-include(CMakeDependentOption)
-
-cmake_dependent_option(BUILD_TESTS
-    "Enable tests" OFF
-    "CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR" ON)
-
 if(NOT TARGET dune::copasi)
   find_package(dune-copasi REQUIRED IMPORTED COMPONENTS Libraries Development Runtime)
 endif()