How to set the locale in RSpec View Examples

I want to test the view to make sure that error messages are properly rendered. My config.default_locale is 'fr'. So, I expect my view to find the proper Active Record error message from my french locale file.

describe 'book/new.html.erb' do
  let(:subject) { rendered }
  before do
    @book = Book.create #this generates errors on my model
    render
  end
  it { should match 'some error message in French' }
end

This test passes when ran in isolation or with the other spec/views. But when I run the full test suite the view gets rendered with the message:translation missing: en.activerecord.errors.models.book.attributes.title.blank.

I don't understand why it renders with an en locale. I tried to force the locale with:

before do
  allow(I18n).to receive(:locale).and_return(:fr)
  allow(I18n).to receive(:default_locale).and_return(:fr)
end

and

before do
  default_url_options[:locale] = 'fr'
end

Does anyone have an idea?