I think we may be talking about the same idea, just in different ways. :-) You did point out something that I didn't mention above in my multiple-config post, though, but I'm not so sure swapping the mapper in different environments is the best way to go. Swapping data sources (from MongoDB to your Memory store) within that mapper based on environment is probably preferable. There may be methods in the mapper used as scopes and you don't want to duplicate that between dev and test environments.

We are definitely going to have to make some Rails-specific considerations for things like environments, though. We might need to create a `perpetuity-rails` gem that extends the functionality of either the Perpetuity module or the Configuration class. And because I like to see example code … :-)

```ruby
Perpetuity.configure do
  environment :test do
    data_source Perpetuity::Memory.new
  end

  environment :development do
    data_source Perpetuity::MongoDB.new(…)
  end
end
```