Write a failing test for reloading with Spring

This test captures what I think is going on in
#323

Currently the factory_bot_rails reloader only reloads factory
definitions when the definition files have changes (using
`execute_if_updated`).

This can cause problems when editing an application file without also
editing a factory_bot definition file. Rails will reload the entire
application, but will not reload the definitions. This causes
factory_bot to have references to classes that were unloaded from the
Rails application and replaced with new classes.

#329 replaces
`execute_if_updated` with `execute` so that factory_bot_rails will
reload the definition files whenever anything in the application is
changed. Hopefully that PR will get this test to pass!

features/reloading.feature

@@ -0,0 +1,63 @@
+Feature:
+  When using factory_bot_rails together with Spring
+  I want changes to my application to trigger the factory_bot_rails reloader
+  So that factory_bot_rails doesn't hold onto stale class references
+
+  Scenario: Editing a model without editing the factory
+    When I successfully run `bundle exec rails new testapp -m ../../features/support/rails_template`
+    And I cd to "testapp"
+    And I add "factory_bot_rails" from this project as a dependency
+    And I add "test-unit" as a dependency
+    And I run `bundle install` with a clean environment
+    And I write to "db/migrate/1_create_users.rb" with:
+      """
+      migration_class =
+        if ActiveRecord::Migration.respond_to?(:[])
+          ActiveRecord::Migration[4.2]
+        else
+          ActiveRecord::Migration
+        end
+
+      class CreateUsers < migration_class
+        def self.up
+          create_table :users do |t|
+            t.string :name
+          end
+        end
+      end
+      """
+    And I run `bundle exec rake db:migrate` with a clean environment
+    And I write to "app/models/user.rb" with:
+      """
+      class User < ActiveRecord::Base
+      end
+      """
+    And I write to "test/factories.rb" with:
+      """
+      FactoryBot.define do
+        factory :author, class: User do
+          name { "Frank" }
+        end
+      end
+      """
+    And I write to "test/unit/user_test.rb" with:
+      """
+      require 'test_helper'
+
+      class UserTest < ActiveSupport::TestCase
+        test "use factory" do
+          author = FactoryBot.create(:author)
+
+          assert_equal author.class.object_id, User.object_id
+        end
+      end
+      """
+    And I run `bundle exec rake test` with Spring enabled
+    And I append to "app/models/user.rb" with:
+      """
+      # User model edited
+      """
+    And I run `bundle exec rake test` with Spring enabled
+    And I run `spring stop` with a clean environment
+    Then the output should contain "1 runs, 1 assertions"
+    And the output should not contain "Failure:"

features/step_definitions/appraisal.rb

@@ -3,3 +3,9 @@
     I successfully run `ruby -e 'system({"BUNDLE_GEMFILE" => nil, "DISABLE_SPRING" => "true"}, "#{command}")'`
   STEP
 end
+
+When /^I run `([^"]+)` with Spring enabled$/ do |command|
+  step <<~STEP
+    I successfully run `ruby -e 'system({"BUNDLE_GEMFILE" => nil}, "#{command}")'`
+  STEP
+end