Rails test setup causing warden's UncaughtThrowError

I'm trying to adapt a pre-devise unit test to make sure that an unconfirmed user is not logged in and is redirected to the sign in page with the devise.failure.unconfirmed message. I keep running into a warden error. I know that I can get rid of the error by confirming the user, but that would defeat the purpose of the test. I believe this version of devise includes the relevant warden test setup in devise's integration_helpers.rb (warden.test_mode!, etc.).

The test code generates: UncaughtThrowError: uncaught throw :warden

The equivalent actions in a localhost:3000 browser generate: 401 with a response body of devise.failure.unconfirmed which displays as expected.

users_controller_test.rb

require 'test_helper'
class UsersControllerTest < ActionDispatch::IntegrationTest
include Devise::Test::IntegrationHelpers
  test "should redirect index when not confirmed" do
    sign_in User.create!(name: 'Bob', email: 'bob@bob.com', password: 'password', password_confirmation: 'password)
    get users_path
  end
end

test_helper.rb

require File.expand_path('../../config/environment',__FILE__)
require 'rails/test_help'

class ActiveSupport::TestCase
  fixtures :all
end

user.rb

class User < ApplicationRecord
  devise :lockable, :confirmable, :database_authenticatable, :registerable, :recoverable, :rememberable, :trackable, :validatable

  validates :name, presence: true, length: { maximum: 50 }
...
end

versions: devise 4.4.1, rails 5.1.4, ruby 2.5.0