Reloading a model in test mode

I have a model which configures some if its associations dynamically
from configuration.

Here's a simplified snippet:
class Article
  (...)
  FacetConfig.facets.each do | f |
    has_many f.name, :class_name => 'PropertyFacet', :conditions =>
{:facet => f.name}
  end
end

In my integration tests I'd like to set up certain FacetConfig
configurations and run test specific to these configurations. However,
changing the config also requires reloading the Article class.

How can I reload a model in test mode? I assume it has to be possible
somehow, as that's what happens in development mode by default.

Thanks in advance!
Simon