> It's the most difficult part of the project I'll agree with that heartily. > the IRS tax code can be consulted to verify the functionality You're not wrong

> It's the most difficult part of the project I'll agree with that heartily. > the IRS tax code can be consulted to verify the functionality You're not wrong, but the problem is often not that. The tax code helps when verifying the system end to end. But it's not like there's one single program that "does the tax" that you can verify that way. The individual bits they're trying to replace are probably more like "fetch all these records from this one mainframe with format X and convert them this way, except if it's Feb 29th in which case fetch it from this other server and convert it another way and then pass it along, except for resident aliens which come from an entirely different place, fetch those from tape storage". This is much harder to get right without formal specs, which there almost certainly aren't. In this case what we have is a "reference implementation" (a.k.a the implementation is the specification), and you can guess how well those go. All this is not to say that they shouldn't have been doing what you're suggesting, but to say that you're making it sound easier than it is now that they're here.