Intentionally produce Errors

[Markus Schiltknecht <markus@xxxxxxxxxx>]

Hi,

this is sort of a silly question, but: what's the proper way to 
intentionally generate an error? I'm writing tests for pyPgSQL and want 
to check it's error handling. Currently, I'm using:

SELECT "THIS PRODUCES AN SQL ERROR";

Is there any better way to generate errors? Probably even generating 
specific errors given?

Regards

Markus