Say I have a Metal class named Preview. How do I test it with RSpec?

When I try:

```
require 'spec_helper'

describe Preview do

  it "should return the posted content" do
    post "/preview", :content => "*title*"
    response.body.should == "*title*"
  end

end

```

I get:

```
undefined method `post' for #<ActiveSupport::TestCase::Subclass_1:0x1058b3098>

```

It seems that RSpec doesn't load up the `:post` method if the test isn't explicitly for a Controller. I've tried specifying `:type => :controller` to no avail.