Sometimes when testing code, it is desirable to not only make sure that the code executes correctly when it should, but also to check that it throws errors or warning when expected. These simple utilities make it easy to test if the expected alerting behavior takes place.

shoulderror: throws an error if the code executes successfully without error.
shouldwarn: throws an error if the code executes without warning.
shouldalert: throws an error if the code executes without either an error or warning.