make using COMMAND in dune_python_add_test an error

cmake/modules/DunePythonTestCommand.cmake

@@ -37,8 +37,12 @@ function(dune_python_add_test)
   include(CMakeParseArguments)
   set(OPTION)
   set(SINGLE WORKING_DIRECTORY NAME)
-  set(MULTI SCRIPT LABELS)
+  set(MULTI SCRIPT COMMAND LABELS)
+  # set(MULTI COMMAND LABELS)
   cmake_parse_arguments(PYTEST "${OPTION}" "${SINGLE}" "${MULTI}" ${ARGN})
+  if(PYTEST_COMMAND)
+    message(FATAL_ERROR "dune_python_add_test: COMMAND argument should not be used, use SCRIPT instead providing only the Python script and not the Python interpreter")
+  endif()
   if(PYTEST_UNPARSED_ARGUMENTS)
     message(WARNING "Unparsed arguments in dune_python_add_test: This often indicates typos!")
   endif()