Rails - Feb 2005 - unit test problem

I checked out the trunk for the first time today to work on a patch.
I''m trying to run the activerecord unit test suite using:

    rake test_mysql_ruby

And I''m getting this error:

/Users/mlovitt/Projects/railstrunk/activerecord/test/../../activesupport/lib/active_support/dependencies.rb:190:in
`require'': No such file to load -- binding_of_caller (LoadError)

I''ve got the active_record unit test databases created, and the latest
version of Ruby and Rake installed.

Any ideas?

Michael