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, :class_name => 'PropertyFacet', :conditions =>
{:facet =>}

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!