I like to use factory test helpers to generate attributes which I then pass to ActiveRecord. The default output is expected to be valid (hence the usage with create-bang below). If you want to override any of the defaults, you can simply use Hash#merge.

Here’s an example, using shoulda. It should be pretty clear how it can be applied to vanilla Test::Unit (or the testing framework du jour ;).

##  I put this in test_helper.rb so I can use it across all tests.
## You could put it in the actual derived test class as well.

  def valid_user_attrs( unique = DateTime.now )
    { :email => "{unique.hash.abs}@example.com", :first_name => "dummy", :last_name => "user_#{unique}", :profile_attributes => valid_profile_attrs }
  end

  def valid_profile_attrs
    ...
  end


## Here’s the actual test case
  
class UserTest < Test::Rails::TestCase

  context "Two Users" do
    setup do
      @user = User.create!( valid_user_attrs )
      @user2 = User.create!( valid_user_attrs.merge( :email => "dummy123@dummy.com" ) )
    end

    should "not be friends" do
      assert !@user.friends.include?( @user2 )
      assert !@user2.friends.include?( @user )
    end

  end
end