Don't abort containt tests when ON_ERROR_STOP is enabled

using the approach from https://stackoverflow.com/a/52744435/674064

5_queries.sql

@@ -86,7 +86,8 @@ ROLLBACK;
 -- Constraints Tests
 
 -- do not alter contents of the database persistently
-BEGIN;
+DO
+$$BEGIN
 
 ALTER TABLE Angestellter
 ADD CONSTRAINT check_Salaer
@@ -96,10 +97,14 @@ UPDATE angestellter SET salaer=30000 where persnr = 1100;
 select * from angestellter WHERE persnr = 1100;
 
 -- forget all changes made since BEGIN
-ROLLBACK;
+EXCEPTION
+WHEN integrity_constraint_violation THEN
+   RAISE NOTICE 'The constraint worked and made the UPDATE fail with message: %', SQLERRM;
+END;$$;
 
 -- do not alter contents of the database persistently
-BEGIN;
+DO
+$$BEGIN
 
 ALTER TABLE ProjektZuteilung
 ADD CONSTRAINT check_Zeitanteil
@@ -109,4 +114,7 @@ UPDATE ProjektZuteilung SET Zeitanteil=99 where persnr = 1100;
 select * from ProjektZuteilung WHERE persnr = 1100;
 
 -- forget all changes made since BEGIN
-ROLLBACK;
+EXCEPTION
+WHEN integrity_constraint_violation THEN
+   RAISE NOTICE 'The constraint worked and made the UPDATE fail with message: %', SQLERRM;
+END;$$;