"@controller is nil" error in ActionController::TestCase

When using context() inside an ActionController::TestCase, I get the following error:

```
RuntimeError: @controller is nil: make sure you set it in your test's setup method.
```

Here is an example of what my test file looks like:

```
class ExamplesControllerTest < ActionController::TestCase
context "index action" do
should "return a list of examples" do
get :index, :format => :json
assert_response :success
end
end
end
```

The error is happening because context() creates a new Test::Unit::TestCase derived class whose name does not contain "ExamplesController", and so Rails becomes confused when it tries to automatically set `@controller` inside of the context() body.

Thanks for your consideration.