globalize plugin makes my tests fail

I installed the globalize plugin to add translation to my app.
However, after following the setup, all my functional tests for all
controllers are failing, including the one's that gor created by
generate scaffold.

Here's an example:

def test_should_show_category
    get :show, :id => 1
    assert_response :success
end

Exception: You have a nil object when you didn't expect it!
The error occured while evaluating nil.code

I think the errors occur because globalize redirects to add the
language code to the url in;

redirect_to params.merge( 'locale' => Locale.base_language.code )

I'm a newbie to ROR and can't figure out how to test around this.