Is there a Lint for ActiveRecord? - ruby-on-rails

Question

Rubyists, particularly Railsers, know all about ActiveModel::Lint, which is a handy way to ensure that you haven't cocked up when writing your ActiveModel subclass, and saves hours of head-scratching. I use it all the time for table-less models in Rails projects.
But I spend a lot of time hunting down errors with my usage of ActiveRecord - particularly with double-sided associations. For example
# app/models/blog.rb
class Blog < ActiveRecord::Base
has_many :posts # so far so good...
end
# app/models/post.rb
class Post < ActiveRecord::Base
has_one :blog # incorrect - should be belongs_to
end
That example is somewhat contrived, as nobody's that silly. But what if Blog actually has a post_id column? Exceptions would not be raised where expected.
I'd like to be able to write a test for Blog like this
# test/unit/blog_test.rb
require 'test/test_helper'
class BlogTest < ActiveSupport::TestCase
include ActiveRecord::Lint
end
...and the test output should say something like Blog :has_many :posts, but Post does not :belong_to :blog!. It would need to reflect on the associations, dealing with table-names, foreign-keys, etc, and considering :through models on the way. I know that proper unit tests will detect these issues anyway, but generally as side-effects of other tests.
Does anyone know of a project which does this? (I'm only interested in ActiveRecord >= 3.1). All I could find was active_record_lint, which doesn't really do this at all.
Additionally, it would be great if all the existing fixtures could be tested automatically, to make sure that those pesky associations are set up. I usually just do
test "fixtures" do
Post.all.each { |p| assert p.valid? "Fixture is broken! #{p.inspect}" }
end
but there's surely a more elegant way.

Answer 1

A tool like this would be useful, but you should be testing these things explicitly anyway. This will uncover problems like this immediately. For instance, a typical unit test:
def test_defaults
blog = Blog.create(
:title => 'Example Blog'
)
assert blog.valid?
assert_equal [ ], blog.errors.full_messages
assert !blog.new_record?
assert_equal 0, blog.posts.count
end
For your post:
def test_defaults
blog = Blog.create(
:title => 'Example Blog'
)
post = Post.create(
:blog => blog,
:content => 'Blogging blog bloggers blogged blogs'
)
assert post.valid?
assert_equal [ ], post.errors.full_messages
assert !post.new_record?
assert_equal blog.id, post.blog_id
assert_equal 1, blog.posts.count
end
Those are the long form versions of some helper methods that I usually use.
If you don't exercise the relationships, you're not testing them and you've got a problem with your test coverage. If you exercise a bad relationship it will show up as an error.