on the same vein, in 2008 we have been contracted by a pharma distribution company to replace it's legacy ERP which worked only with DOS. To prove the new ERP is working we had to reproduce the reports from the legacy system bug for bug with the exact same numbers. On my linux workstation, I installed dosbox, a copy of their software and database, and made scripts that exported the data by printing the screen then compared the old and new reports. I did that till I got the reports right. proper TDD.