Add tests for OAuth2

test/factories/oauth_applications.rb

@@ -0,0 +1,8 @@
+FactoryBot.define do
+  factory :oauth_application, :class => "Doorkeeper::Application" do
+    sequence(:name) { |n| "OAuth application #{n}" }
+    sequence(:redirect_uri) { |n| "https://example.com/app/#{n}" }
+
+    association :owner, :factory => :user
+  end
+end