Rails - Jun 2006 - Testing association definitions...

Are there best practices for testing that the model class declares  
the appropriate association linkages?   Similarly are there good ways  
to test that the model has declared desired acts_as_[list |  tree]?

My first thought was to simply test if the model respond_to? either a  
characteristic method of the association or even a more complete list  
of methods.  This would seem to be in-line with duck-typing, but it  
also feels a little cumbersome.  So how do you test-drive your  
association linkages?

Eric