How to handle error message in PG_CATCH

I'm working on implementing pg_check functions. Because I want to test 
whole table I need catch a error and handle it myself. I use following 
construct:



PG_TRY();
{...ereport(ERROR, (errmsg("Error test")));...
}
PG_CATCH();
{errcontext("Context error");        EmitErrorReport();        FlushErrorState();
}
PG_END_TRY();

At the end I got following message:

ERROR:  Error test
CONTEXT:  Context error
server sent data ("D" message) without prior row description ("T" message)

and also nothing appears in a log file. Similar concept is used in
autovacuum.c.

Any idea what is wrong?
    Thanks for help Zdenek