FND_FUCTION.TEST(Function_Name)

Test if function is accessible under current responsibility.TRUE if function is accessible.

This function Only checks static function security, and global object type grants from data security.  
Because this routine does not take the object id and instance pks, it cannot test for most data security grants, and therefore it should not be used if the object id and/or instance pks are known.
This is here for cases where performance is critical, and for backwards compatibility, but in general new code should use TEST_INSTANCE instead if acting on a particular object instance (database row).

Example

There is function:HELLOWORLD,which is under Inventory responsibility.

BEGIN
  fnd_global.apps_initialize(user_id      => 1068,
                             resp_id      => 21623, --Order Management Super User responsibility
                             resp_appl_id => 401);
                             
  IF fnd_function.test(\'HELLOWORLD\') THEN
    dbms_output.put_line(\'TRUE\');
  ELSE
    dbms_output.put_line(\'FALSE\');
  END IF;
END;

Output:False

If change resp_id to inventory ID,Output will be TRUE.

Check Oracle Application Developer Guide for API details(Chapter 11)