How to trigger the warning % of number range

Hi experts,

I've created a Z number range z_text,and setted 50% to Warning %.

And then called function NUMBER_GET_NEXT in program,but sy-subrc always equal to 0.

DATA num TYPE n LENGTH 3.
CALL FUNCTION 'NUMBER_GET_NEXT'
EXPORTING
nr_range_nr = '01'
object = 'Z_TEST'
* QUANTITY = '1'
* SUBOBJECT = ' '
* TOYEAR = '0000'
* IGNORE_BUFFER = ' '
IMPORTING
number = num
* QUANTITY =
* RETURNCODE =
EXCEPTIONS
interval_not_found = 1
number_range_not_intern = 2
object_not_found = 3
quantity_is_0 = 4
quantity_is_not_1 = 5
interval_overflow = 6
buffer_overflow = 7
OTHERS = 8.
IF sy-subrc <> 0.
MESSAGE ID sy-msgid TYPE sy-msgty NUMBER sy-msgno
WITH sy-msgv1 sy-msgv2 sy-msgv3 sy-msgv4.
ENDIF.

So how to trigger the warning % of number range,and in what form we received the warning % .

Best Regards.