Need some help with some tests for a critical core patch

I'm not that familiar with the fixtures setup in the core code and as a result have been having problems coming up with a test that can accompany the following patch. Is there someone who would be willing to help me put one together?

From the description:

"There's a problem with eager loading when one of the associations is nil.

I first noticed it with an :include => [:actor, {:link => :my_links}, {:url_tags => :tag}] on an AR class called Memo. It failed when it couldn't find the :my_links on Memo!? Clearly :my_links is wrt. the Memo#link target (a Link).

So what was causing the problem? Turned out that for one of the Memo instances the :link association was nil. Fine, it's an optional attribute... But when I tracked it down, it was caused by the recursion in JoinDependency#construct being blocked by the nil value. Since the recursion is matched by the flattened list of association names in the join array, it is necessary to complete the recursion (i.e. recurse down through Link#my_links) even when the instantiated Memo#link value is nil. We must simply not construct the instantiated associations while so recursing."