how to check type of value in postgres

I want to check type of value in postgres like this:

SELECT id,
       CASE 
         WHEN val_is_integer THEN (SOME_QUERY)
         WHEN val_isnot_integer THEN (ANOTHER_QUERY)
         ELSE 0
       END
  FROM test;

How to do that?

notes: the value is varchar type in table, and in that field there is value is numeric and varchar ...

example:

ID | value
1 | test
2 | 10
3 | 12
4 | test123