Unable to run tests for acts_as_nested_set

Hi,

I have acts_as_nested_set installed in my app under vendor/plugins.
When I run 'rake test:plugins' I get the following error:

/usr/bin/ruby1.8 -Ilib:test "/var/lib/gems/1.8/gems/rake-0.8.1/lib/
rake/rake_test_loader.rb" "vendor/plugins/acts_as_nested_set/test/
nested_set_test.rb"
/var/lib/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:275:in `load_missing_constant': uninitialized constant
ActiveRecord::Acts (NameError)
  from /var/lib/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:467:in `const_missing'
  from ./vendor/plugins/acts_as_nested_set/test/../init.rb:1
  from /usr/lib/ruby/1.8/rubygems/custom_require.rb:27:in
`gem_original_require'
  from /usr/lib/ruby/1.8/rubygems/custom_require.rb:27:in `require'
  from /var/lib/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:509:in `require'
  from /var/lib/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:354:in `new_constants_in'
  from /var/lib/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:509:in `require'
  from ./vendor/plugins/acts_as_nested_set/test/nested_set_test.rb:7
  from /var/lib/gems/1.8/gems/rake-0.8.1/lib/rake/rake_test_loader.rb:
5:in `load'
  from /var/lib/gems/1.8/gems/rake-0.8.1/lib/rake/rake_test_loader.rb:5
  from /var/lib/gems/1.8/gems/rake-0.8.1/lib/rake/rake_test_loader.rb:
5:in `each'
  from /var/lib/gems/1.8/gems/rake-0.8.1/lib/rake/rake_test_loader.rb:5
rake aborted!
Command failed with status (1): [/usr/bin/ruby1.8 -Ilib:test "/var/lib/
gems...]

I am not sure if this is:
1) Something I am doing wrong
2) A problem with acts_as_nested_set
3) A problem with rails plugins in general

I am running with a recent git version in vendor/rails, although the
gem version of active support shows up in that trace for some reason.

Thanks in advance for any assistance.