Hi David,
  I should have read your earlier comment. I took a quick glance, it seems the aws-sdk is not doing method_messing or anything wicked there, just normal meta programming. So the RDS Client object should have that method defined. My gut reaction is we should be cautious about turning some of the double's into instance_double's because we lose some of the typing protection there. We also won't likely have integration test for this feature, which increases the area with little coverage hidden under a conditional.

Jesse