A really smelly, but working way to mock test Active Record chained queries in Rails 3.

rspec_mock_rails3_chained_queries.rb

# @session and @mock_project instance variables are defined elsewhere.
before(:each) do
  joins = mock(ActiveRecord::Relation)
  ProjectUser.should_receive(:joins).with(:project_user_datum).and_return(joins)
  joins.should_receive(:where).
    with('project_user_data.project_id = :project_id', { :project_id => @mock_project }).
    and_return(@mock_project)
  get :index, {}, @session
end