昔のRailsではsecret_key_baseの設定が必須だった

```
  3) HealthCheck /custom_route_prefix fails with smtp server and invalid custom_check
     Failure/Error: get '/custom_route_prefix'

     RuntimeError:
       Missing `secret_key_base` for 'test' environment, set this value in `config/secrets.yml`
     # ./spec/health_check_spec.rb:24:in `block (4 levels) in <top (required)>'
     # ./spec/spec_helper.rb:24:in `start_smtp_server'
     # ./spec/health_check_spec.rb:23:in `block (3 levels) in <top (required)>'
```

spec/dummy/fake_app.rb

@@ -4,6 +4,7 @@
 FakeApp.config.root = File.dirname(__FILE__)
 FakeApp.config.action_mailer.delivery_method = :smtp
 FakeApp.config.action_mailer.smtp_settings = { address: "localhost", port: 3555, openssl_verify_mode: OpenSSL::SSL::VERIFY_NONE, enable_starttls_auto: true }
+FakeApp.config.secret_key_base = SecureRandom.hex(64)
 FakeApp.initialize!