Rails 5.1 requires ActionController::TestRequest to have a controller class

Pass it in as an anonymous class

test/integration/rememberable_test.rb

@@ -10,7 +10,13 @@ class RememberMeTest < Devise::IntegrationTest
   end
 
   def generate_signed_cookie(raw_cookie)
-    request = Devise.rails5? ? ActionDispatch::TestRequest.create : ActionDispatch::TestRequest.new
+    request = if Devise.rails51?
+      ActionController::TestRequest.create(Class.new) # needs a "controller class"
+    elsif Devise.rails5?
+      ActionController::TestRequest.create
+    else
+      ActionController::TestRequest.new
+    end
     request.cookie_jar.signed['raw_cookie'] = raw_cookie
     request.cookie_jar['raw_cookie']
   end

test/rails_app/config/boot.rb

@@ -3,7 +3,11 @@ unless defined?(DEVISE_ORM)
 end
 
 module Devise
-  # Detection for minor differences between Rails 4 and 5 in tests.
+  # Detection for minor differences between Rails 4 and 5, and 5.1 in tests.
+  def self.rails51?
+    Rails.version.start_with? '5.1'
+  end
+
   def self.rails5?
     Rails.version.start_with? '5'
   end

test/test/controller_helpers_test.rb

@@ -163,7 +163,15 @@ class TestControllerHelpersTest < Devise::ControllerTestCase
 
   test "creates a new warden proxy if the request object has changed" do
     old_warden_proxy = warden
-    @request = Devise.rails5? ? ActionController::TestRequest.create : ActionController::TestRequest.new
+
+    @request = if Devise.rails51?
+      ActionController::TestRequest.create(Class.new) # needs a "controller class"
+    elsif Devise.rails5?
+      ActionController::TestRequest.create
+    else
+      ActionController::TestRequest.new
+    end
+
     new_warden_proxy = warden
 
     assert_not_equal old_warden_proxy, new_warden_proxy