Coverage isn't reported correctly for Mongoid backed rails project

[singfoom]

I've got a rails project that's using Mongoid as the "database" and I'm getting odd coverage results. Here's a snippet of a good example of the behavior I'm seeing:

Class:

 class Source::TwitterFeed < Source
  field :hash_tags, :type => Array, :default => []
  field :users, :type => Array, :default => []
  attr_accessible :users, :hash_tags

  validate :validate_empty_feed

  def validate_empty_feed
    if (self.users.empty? && self.hash_tags.empty?)
      errors.add(:users, "must have at least one username or hash_tag")
    end
  end

Test

context "twitter feed with empty hash_tags and users validation" do
  setup do
    Source::TwitterFeed.delete_all
    @twitter_feed = Source::TwitterFeed.create(:users => [], :hash_tags => [])
  end

  should "be invalid" do
    assert(@twitter_feed.invalid?, "twitter_feed was not invalid")
  end
end

The test passes. Yet, only the def line of validate_empty_feed is considered covered. For reference, this is with cover_me 1.0.0, rails 3.0.7 and a cover_me config (That's really just empty) after a require in the test helper. I see this behavior all over the coverage report, where I have tests that I'm sure execute lines but are not considered covered. I looked around at the other issues and googled around but was unable to find anything on cover_me and mongoid.

[singfoom]

I wanted to add that I have another test inside that context that hits the internals of that method more clearly.

should "have errors on users" do
  assert_equal(@twitter_feed.errors, {:users => ["must have at least one username or hash_tag"]})
end

This also passes and has the coverage problems I've mentioned earlier.

[dougrohde]

I have noticed the same problem as well. For example, for a particular method that I'm sure is being run, but does not show as covered, I'll throw a raise statement somewhere in that method and get errors all over the place when I run my tests. When I remove it, though, it still shows as not being covered.