'eval_block' shouldn't be used since it is a private API.

This method was made private on Rails master @ d2d3376903

test/routes_test.rb

@@ -242,9 +242,10 @@ class CustomizedRoutingTest < ActionController::TestCase
 
   test 'checks if mapping has proper configuration for omniauth callback' do
     e = assert_raise ArgumentError do
-      @routes.dup.eval_block -> {
+      routes = ActionDispatch::Routing::RouteSet.new
+      routes.draw do
         devise_for :not_omniauthable, class_name: 'Admin', controllers: {omniauth_callbacks: "users/omniauth_callbacks"}
-      }
+      end
     end
     assert_match "Mapping omniauth_callbacks on a resource that is not omniauthable", e.message
   end