In order to create a test user with password instead of <peer authentication>, let's create test user:
``
createuser -P user0
createdb user0
``
`-P` makes it prompt for the users password.

Alternatively, to create the password non-interactively https://stackoverflow.com/questions/42419559/postgres-createuser-with-password-from-terminal[]:
``
psql -c "create role NewRole with login password 'secret'"
``
Can't find a way using the `createuser` helper.

We can then login with that password with:
``
psql -U user0 -h localhost
``
which asks for the password we've just set, because the `-h` option turns off peer authentication, and turns off password authentication.

The password can be given non-interactively as shown at https://stackoverflow.com/questions/6405127/how-do-i-specify-a-password-to-psql-non-interactively with the `PGPASSWORD` <environment variable>:
``
PGPASSWORD=a psql -U user0 -h localhost
``

Now let's create a test database which `user0` can access with an existing superuser account:
``
createdb user0db0
psql -c 'GRANT ALL PRIVILEGES ON DATABASE user0db0 TO user0'
``

We can check this permission with:
``
psql -c '\l'
``
which now contains:
``
                                  List of databases
   Name    |  Owner   | Encoding |   Collate   |    Ctype    |   Access privileges
-----------+----------+----------+-------------+-------------+-----------------------
 user0db0  | ciro     | UTF8     | en_GB.UTF-8 | en_GB.UTF-8 | =Tc/ciro             +
           |          |          |             |             | ciro=CTc/ciro        +
           |          |          |             |             | user0=CTc/ciro
``
The permission letters are explained at:
* https://www.postgresql.org/docs/13/ddl-priv.html
* https://stackoverflow.com/questions/25691037/postgresql-permissions-explained/25691587

`user0` can now do the usual table operations on that table:
``
PGPASSWORD=a psql -U user0 -h localhost user0db0 -c 'CREATE TABLE table0 (int0 INT, char0 CHAR(16));'
PGPASSWORD=a psql -U user0 -h localhost user0db0 -c "INSERT INTO table0 (int0, char0) VALUES (2, 'two'), (3, 'three'), (5, 'five'), (7, 'seven');"
PGPASSWORD=a psql -U user0 -h localhost user0db0 -c 'SELECT * FROM table0;'
``


Discussion on "Create a test user in PostgreSQL" by Ciro Santilli 32