errors after applying validtation in rails app

when i implemented regex validation in username field in models of rails app everything works fine locally but on github this pull request fails in appveyor tests

          format: { with: /A[a-zA-Z_ ]{2,30}z/,
          message: ":can contain only alphabets,underscores and spaces" },
          on: :create

i think the errors are due to existing users..
here is the link of log file of appveyor test and link of pull request