How would you test an object-oriented design’s sequence diagrams? Could you Be bit specific.

I would test their flight ability by folding them up into a nonstandard paper airplane and dropping them out the window.

To be specific, I would scrap the idea of sequence diagrams altogether; if your design is so complicated that it needs sequence diagrams, you're relying too much on state-modifying operations and need to improve the design a bit -- or at the very least you're bad at encapsulation and your sequence diagram shouldn't be big enough that you feel the need to "test" it.