set the configured #inheritance_column on #become (#7503)

I had to create a new table because I needed an STI table,
which does not have both a "type" and a "custom_type"

the test fails with:
  1) Error:
test_alt_becomes_works_with_sti(InheritanceTest):
NoMethodError: undefined method `type=' for #<Cabbage id: 1, name: "my cucumber", custom_type: "Cucumber">
    /Users/username/Projects/rails/activemodel/lib/active_model/attribute_methods.rb:432:in `method_missing'
    /Users/username/Projects/rails/activerecord/lib/active_record/attribute_methods.rb:100:in `method_missing'
    /Users/username/Projects/rails/activerecord/lib/active_record/persistence.rb:165:in `becomes'
    test/cases/inheritance_test.rb:134:in `test_becomes_works_with_sti'
    test/cases/inheritance_test.rb:140:in `test_alt_becomes_works_with_sti'

1 files changed, 9 insertions, 1 deletions

diff --git a/activerecord/test/cases/inheritance_test.rb b/activerecord/test/cases/inheritance_test.rb
index e80259a7f1..cc9a93c16f 100644
--- a/activerecord/test/cases/inheritance_test.rb
+++ b/activerecord/test/cases/inheritance_test.rb
@@ -5,9 +5,10 @@ require 'models/post'
 require 'models/project'
 require 'models/subscriber'
 require 'models/teapot'
+require 'models/vegetables'
 
 class InheritanceTest < ActiveRecord::TestCase
-  fixtures :companies, :projects, :subscribers, :accounts
+  fixtures :companies, :projects, :subscribers, :accounts, :vegetables
 
   def test_class_with_store_full_sti_class_returns_full_name
     old = ActiveRecord::Base.store_full_sti_class
@@ -127,6 +128,13 @@ class InheritanceTest < ActiveRecord::TestCase
     switch_to_default_inheritance_column
   end
 
+  def test_alt_becomes_works_with_sti
+    vegetable = Vegetable.find(1)
+    assert_kind_of Vegetable, vegetable
+    cabbage = vegetable.becomes(Cabbage)
+    assert_kind_of Cabbage, cabbage
+  end
+
   def test_inheritance_find_all
     companies = Company.all.merge!(:order => 'id').to_a
     assert_kind_of Firm, companies[0], "37signals should be a firm"