rspec & rails 3 cannot find model object

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?
    开发者_StackOverflow社区  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?

Seems in rails 3 I need to require 'spec_helper'

require 'spec_helper'

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

But that might just be because I'm running it from rake spec if you're using watchr or some other mechanism you might be able to get that done for you.