It is automated spaghetti-code generation. When each object has an internal state machine that sends and receives messages to other objects that have their own

It is automated spaghetti-code generation. When each object has an internal state machine that sends and receives messages to other objects that have their own state machines, it creates a mess of tightly-coupled code that is difficult to test and maintain. This "object-oriented" method did not become more popular because there are better ways to do it. I worked on a system that was built using a Shlaer-Mellor code generation tool and the code was a nightmare to maintain because it was a mess of tightly-coupled state machines with numerous circular dependencies. Want to test a single class? Okay, create mocks for almost all the other classes.