postgresql – How to use ASSERT to confirm the value of `current_user`

While building up my schema (i.e., dev mode), I would like to use ASSERT to “confirm” that I’m doing what I think I’m doing.

I tried to use

create function api.login(...)
    returns void
    language plpgsql
    as $$
        declare
            ...
        begin
            ...
            ASSERT current_user::text = "anonymous", 'Unexpected user';
            ...
        end;
    $$;

Postgres renders the clause as a select statement and reports the error that column "anonymous" does not exist. Right now, that’s throwing me a bit given the like:

select (2 + 2 = 4)
> t

-- this does not generate an error
select current_user = 'db_user'
> t

I’m new to using Postgres (a. what took me so long?! b. and using sql outside of data processing :)), so would greatly appreciate learning the best way to assert the user is what I think it is (not to mention, conveying the security intent).

Thank you in advance!