Use this instruction for conditional compilation within the ST editor.
#IF IsSystemVariableSupported('sys_bIsPlcInTestMode') <> 0 #THEN
(*condition TRUE: first part is compiled and executed*)
#ELSE
(*condition FALSE: second part is compiled and executed*)
OutputCompilerWarning('PLC does not support the test mode');
#END_IF;
This code with an S PLC returns the following warning: