new to tests, how to get info on asset results

hey.
I'm about 2 years into using rails and just discovering tests.
Im writing some unit tests. its all going well.

one thing i'm wondering about, When i run an assert 'whatever' unit test, is there any way to get any Error messages..
example

a model that has 'validates_presense_of :whatever'

and then a test to save a record for that model where there is no :whatever, that will = false

if i say assert model.save, and that will generate a failure, can i get the error / reason why its failed?
thanks!