Rails3: Find method not working with fixtures in test environment

Question

The Rails Guide says, "Fixtures can also transform themselves into the form of the original class. Thus, you can get at the methods only available to that class," and gives the example,

# using the find method, we grab the "real" david as a User 
david = users(:david).find 

My fixtures are working ok, but when I try

    memb = members(:one).find

I get an error: NoMethodError: undefined method `find'. What am I doing wrong?

(Rails Guide reference: http://edgeguides.rubyonrails.org/testing.html#the-low-down-on-fixtures)