How to catch an user defined error message

Recently I am working on a project. In this project, there is a database package in which I put all the related functions and procedures. I want a function to generate user defined errors while calling it directly in the hosting environment; meanwhile, I want the calling stored procedure to ignore some of the user generated errors if the function is being called by a stored procedure. The point here is to catch some user defined errors but not the oracle predefined errors.

There is a RAISE_APPLICATION_ERROR statement in the function to generate the user defined error. e.g.

function test
return number
is
e_no_rate_found exception;
begin
raise e_no_rate_found;
exception
when e_no_rate_found then
raise_application_error(-20306, 'No rate found!');
end;

If this function is called directly from sqlplus, the user defined error -20306 will be raised. I want to ignore this error in a procedure which calls this function. Actually, it's same to catch an user defined error as to catch an oracle predefined error. Here we go. In the procedure, we could write the code block below:

declare
e_no_rate_found exception;
pragma exception_init(e_no_rate_found, -20306);
begin
call test;
exception
when e_no_rate_found then
NULL;
end;

The user defined error -20306 is associated with the user defined exception e_no_rate_found using exception_init pragma in the calling procedure.