Allow custom domain transfer code

#660

app/models/concerns/domain/transferable.rb

@@ -2,7 +2,7 @@ module Concerns::Domain::Transferable
   extend ActiveSupport::Concern
 
   included do
-    after_initialize :generate_transfer_code, if: :new_record?
+    after_initialize :generate_transfer_code, if: 'new_record? && transfer_code.blank?'
   end
 
   def transfer(new_registrar)

test/models/domain_transfer_test.rb

@@ -5,18 +5,20 @@ class DomainTest < ActiveSupport::TestCase
     @domain = domains(:shop)
   end
 
-  def test_rejects_absent_transfer_code
+  def test_invalid_without_transfer_code
     @domain.transfer_code = nil
     @domain.validate
     assert @domain.invalid?
   end
 
-  def test_generates_random_transfer_code_if_domain_is_new
+  def test_generates_default_transfer_code
+    domain = Domain.new
+    refute_empty domain.transfer_code
+  end
+
+  def test_generated_transfer_code_is_random
     domain = Domain.new
     another_domain = Domain.new
-
-    refute_empty domain.transfer_code
-    refute_empty another_domain.transfer_code
     refute_equal domain.transfer_code, another_domain.transfer_code
   end
 
@@ -27,6 +29,11 @@ class DomainTest < ActiveSupport::TestCase
     assert_equal original_transfer_code, @domain.transfer_code
   end
 
+  def test_overrides_default_transfer_code
+    domain = Domain.new(transfer_code: '1bad4f')
+    assert_equal '1bad4f', domain.transfer_code
+  end
+
   def test_changes_registrar
     old_transfer_code = @domain.transfer_code
     new_registrar = registrars(:goodnames)