I'll give you the full story.

The only way I could reproduce the reported bug was by ensuring that the planner never finds goal states. This is why I have a test for DubinsWithoutGoalBias. That's the case I'm checking for in the above test.

The issue is that, when RRTstar has not found a goal state yet, you can think of it as only optimizing paths for distance from goal. This means that, as long as the planner has not found a goal state yet, it's possible that the planner's so-far best solution can in fact increase in path cost over time.

I think this is fine behavior for RRTstar, so I didn't want to penalize that in the NoGoalBiasTest.