Excellent observations, @lgibbs!
While I find it troubling that testability still has to be “sold” at a time when many want new and updated products introduced rapidly, I understand and appreciate the questions of cost and business value. When I define testability as improved control over inputs and improved observability of outputs, I offer the following.
In my opinion, the cost of testability delivers business value to all stakeholders. Initially, the transparency afforded by improved testability assists product development by providing information about the behavior of transactions. The testability may have reduced defects that could have otherwise gone unnoticed. It could also reduce testing time.
As the project continues and the product grows, the testabiity begins to assist developers in both transaction development and troubleshooting. This could result in a higher quality product that allows the testing team to explore risks more than requirements.
Finally, after the product is deployed, the testability (using mostly improved observability of outputs) assists in troubleshooting production issues. This could result in quicker resolutions that should delight any product manager.
Joe