While the built-in tests are interesting, you can use pgbench instead as a testing harness to run your own database tests. This gets you multiple clients running at once, executing concurrent queries with a minimum of scripting.
To give an idea how this might be useful, imagine you want to test how fast your system can write data to disk using
INSERT. You might copy the filler concept from the built-in tables, where you just want to create some strings with a particular length and therefore size in bytes, without caring about the content (this is included in
create table data(filler text);
But then create a custom script that actually fills that much space up (also included ...