what happens when "rake test"?

Hello,     I meet a problem which become a stopper. When I run "rake test" . then there always comes the error :

D:/InstantRails/ruby/lib/ruby/1.8/csv.rb:11: CSV is not a class (TypeError)

my enviroment is Rails1.2.1+Ruby1.8.4. The same issue can be reproduced in the same code in Rails1.2.2+Ruby1.8.5

currently i can comments this then all works.

c:\ruby\lib\ruby\gems\1.8\gems\activerecord-1.15.2\lib\active_record \fixtures.rb (line 3)     require 'csv'

but what i think this is a damage to the project.

what I am interested is , what happens when i run "rake test"? i would like to debug into the source code to see what is going on and why there is such bug.