fix user_controller_spec when testing too long usernames

spec/controllers/users_controller_spec.rb

@@ -637,7 +637,7 @@ describe UsersController do
 
       context 'is too long' do
         before do
-          xhr :get, :check_username, username: 'abcdefghijklmnop'
+          xhr :get, :check_username, username: generate_username(User.username_length.last + 1)
         end
         include_examples 'checking an invalid username'
 

spec/spec_helper.rb

@@ -146,6 +146,11 @@ def create_post(args={})
   PostCreator.create(user, args)
 end
 
+def generate_username(length=10)
+  range = [*'a'..'z']
+  Array.new(length){range.sample}.join
+end
+
 module MessageBus::DiagnosticsHelper
   def publish(channel, data, opts = nil)
     id = super(channel, data, opts)