In my experience, it's pretty difficult, particularly in middleware code that passes values received from one part of the code to another. There was a lot of c

In my experience, it's pretty difficult, particularly in middleware code that passes values received from one part of the code to another. There was a lot of code tracing, both up the stack - to figure out where the values are actually coming from, or down the stack - to figure out what the code that ultimately uses them is expecting. I ended up leaning on interactive debugger sessions pretty heavily, since you can peek at what kinds of value are actually going through the system, but that tends to emphasis the "happy path cases" and it can be harder to track down the edge cases.