rspec model class methods

I've started specifying a project and could use some help. I'm not sure
if the spec is entirely necessary, it would be great to get some
guidance on a best practice or something close.

I recently realized the need to add the method below grouped_by_months
and started to write a spec.

idea 1:
{{{
  before do
    @comment = Comment.new
    @comment.stub!(:created_at).and_return(Time.now -2.days)
  end

  it 'should return comments grouped by month' do
    group_terms = lambda{|comment| comment.created_at.beginning_of_month
}

    Comment.should_receive(:find).and_return([@comment])
    [@comment].should_receive(:group_by).with(&group_terms).and_return([[@comment]])

    Comment.grouped_by_month
  end
}}}

idea 2
{{{

  before do
    @comment = Comment.new
    @comment.stub!(:created_at).and_return(Time.now -2.days)
  end

  it 'should return comments grouped by month' do
group_terms = lambda{|comment| comment.created_at.beginning_of_month }
    lambda{
      Comment.should_receive(:find).and_return([@comment])
    }.should_receive(:group_by).with(&group_terms)

Comment.grouped_by_month
end
}}}

Class with method
{{{
class Comment < ActiveRecord::Base

  validates_presence_of :email, :body
  validates_format_of :email, :with =>
/\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\Z/i, :message => 'invalid
email address'

  def self.grouped_by_month
    find(:all).group_by{|comment| comment.created_at.beginning_of_month
}
  end

end
}}}