Fix added tests for sign_in_after_reset_password per resource class

We can't just "swap" those model properties, as that sets instance vars
on the classes that get reverted to their "previous" value, which ends
up leaving the instance vars set as `nil`. However, our logic for those
model/class properties actually checks for `defined?` as a way to
override them, and delegates up to `Devise` global config if they are
not defined, so leaving instance vars back with `nil` values isn't
enough, we need to actually remove them.

This introduces a new test helper specifically for overriding those
model configs so that we can do proper cleanup.

test/integration/recoverable_test.rb

@@ -223,7 +223,7 @@ class PasswordTest < Devise::IntegrationTest
   end
 
   test 'does not sign in user automatically after changing its password if resource_class.sign_in_after_reset_password is false' do
-    swap User, sign_in_after_reset_password: false do
+    swap_model_config User, sign_in_after_reset_password: false do
       create_user
       request_forgot_password
       reset_password
@@ -237,7 +237,7 @@ class PasswordTest < Devise::IntegrationTest
 
   test 'sign in user automatically after changing its password if resource_class.sign_in_after_reset_password is true' do
     swap Devise, sign_in_after_reset_password: false do
-      swap User, sign_in_after_reset_password: true do
+      swap_model_config User, sign_in_after_reset_password: true do
         create_user
         request_forgot_password
         reset_password

test/support/helpers.rb

@@ -73,6 +73,17 @@ class ActiveSupport::TestCase
     end
   end
 
+  def swap_model_config(model, new_values)
+    new_values.each do |key, value|
+      model.send :"#{key}=", value
+    end
+    yield
+  ensure
+    new_values.each_key do |key|
+      model.remove_instance_variable :"@#{key}"
+    end
+  end
+
   def clear_cached_variables(options)
     if options.key?(:case_insensitive_keys) || options.key?(:strip_whitespace_keys)
       Devise.mappings.each do |_, mapping|