ORA-00932: inconsistent datatypes: expected – got CLOB

You can’t put a CLOB in the WHERE clause. From the documentation:

Large objects (LOBs) are not supported in comparison conditions.
However, you can use PL/SQL programs for comparisons on CLOB data.

If your values are always less than 4k, you can use:

UPDATE IMS_TEST 
   SET TEST_Category           = 'just testing'  
 WHERE to_char(TEST_SCRIPT)    = 'something'
   AND ID                      = '10000239';

It is strange to search by a CLOB anyways.. could you not just search by the ID column?