add username to user factory

spec/factories/user.rb

@@ -1,6 +1,7 @@
 FactoryBot.define do
   factory :user do
     sequence(:email_address) { |n| "user#{n}@example.com" }
+    sequence(:username) { |n| "user#{n}" }
     password_digest { BCrypt::Password.create('password123') }
   end
 end