I'm trying to put some specs around a new rails 3 project I am working on, and my first test doesn't seem to be able to find a model.

I've installed rspec from the command line using:

sudo gem install rspec --pre

and then I put the following in my Gemfile

gem "rspec-rails", ">= 2.0.0.beta.1"

But when I run my test I get

./spec/models/world_spec.rb:1: uninitialized constant World (NameError)
rake aborted!
Command /opt/local/bin/ruby  -Ilib -Ispec "./spec/models/world_spec.rb" failed
/opt/local/lib/ruby/gems/1.8/gems/rspec-core-2.0.0.beta.4/lib/rspec/core/rake_task.rb:71:in `define'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:1112:in `verbose'
/opt/local/lib/ruby/gems/1.8/gems/rspec-core-2.0.0.beta.4/lib/rspec/core/rake_task.rb:57:in `send'
/opt/local/lib/ruby/gems/1.8/gems/rspec-core-2.0.0.beta.4/lib/rspec/core/rake_task.rb:57:in `define'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `call'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `execute'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `each'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `execute'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:597:in `invoke_with_call_chain'
/opt/local/lib/ruby/1.8/monitor.rb:242:in `synchronize'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:583:in `invoke'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2051:in `invoke_task'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `top_level'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `each'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `top_level'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2023:in `top_level'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2001:in `run'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:1998:in `run'
/opt/local/lib/ruby/gems/1.8/gems/rake-0.8.7/bin/rake:31
/opt/local/bin/rake:19:in `load'
/opt/local/bin/rake:19

My spec is in spec/models/world_spec.rb, and looks like

    describe World, "#hello" do
      it "should be invalid" do
        World.new.should be_invalid?
      end
    end

I tried adding a line like require "app/model/world" and require "world" but to no success.

Does anyone know what I'm doing wrong?