```ruby
require File.dirname(__FILE__) + '/helper.rb'

class TestBelongsToAssociation < ActiveSupport::TestCase
  class Main < ActiveRecord::Base
  end

  class Other < ActiveRecord::Base
    belongs_to :main, :inherit => :account_id
  end

  def test_value_is_inherited_from_parent
    @main = Main.create!(:account_id => 42)
    @other = Other.create!(:main => @main)

    assert_equal 42, @other.account_id
  end
end
```

Add a few more tests
user
```ruby
require File.dirname(__FILE__) + '/helper.rb'

class TestBelongsToAssociation < ActiveSupport::TestCase
  class Main < ActiveRecord::Base
  end

  class Other < ActiveRecord::Base
    belongs_to :main, :inherit => :account_id
  end

  def test_value_is_inherited_from_parent
    @main = Main.create!(:account_id => 42)
    @other = Other.create!(:main => @main)

    assert_equal 42, @other.account_id
  end

  def test_does_not_inherit_when_parent_not_present
    @other = Other.create!
    assert_nil @other.account_id
  end

  def test_overwrites_value_on_child
    @main = Main.create!(:account_id => 42)
    @other = Other.create!(:main => @main, :account_id => 1337)

    assert_equal 42, @other.account_id
  end
end
```
assistant