Here is how to create deadlocks in PostgreSQL for testing purposes:

1. Open 2 sessions logged in with the same account in PostgreSQL.

2. In session 1, type the following:

   SET deadlock_timeout = '1h';
   BEGIN;
   SELECT * FROM users WHERE id = 100 FOR UPDATE:
   

   NOTE: The default deadlock_timeout is 1s. You can also set it at 5min instead of 1h to keep it more reasonable.

3. In Session 2, type the following:

   SET deadlock_timeout = '1h';
   BEGIN;
   SELECT * FROM users WHERE id = 200 FOR UPDATE:
   

4. In Session 1, type the following:

   SELECT * FROM users WHERE id = 200 FOR UPDATE:
   

   A block occurs after trying to execute this query.

5. In Session 2, type the following:

   SELECT * FROM users WHERE id = 100 FOR UPDATE:
   

   A block occurs after trying to execute this query.