When the forebears of SystemVerilog and UVM were being created, the world was a different place. Verification was primarily directed testing and code coverage was good enough to signal completion. Development of directed tests was getting to be slow, cumbersome and difficult to maintain. Languages and tools were created that added the ability to randomize stimulus but that created two problems. First, you had no idea what a test had accomplished and second, you had no idea that the design had actually reacted in the right manner. Thus, two additional models became necessary: a combination of checkers and scoreboard and the coverage model. The big problem was, and remains, that the three models are independent models only unified by a thin layer of syntax. (more…)