I consider myself an advocate of sequence diagrams (of all other UML diagrams), so I wonder why the article doesn't mention that this type of diagrams is meant

I consider myself an advocate of sequence diagrams (of all other UML diagrams), so I wonder why the article doesn't mention that this type of diagrams is meant to depict testable flows the software components. It's nice and all that you can clarify to your team what you want to gain (the big picture), and it's also nice if you want to explain how (details), but in my opinion it's not worth much if your sequence diagram doesn't explain test cases clearly and expect for them to be written.