> That’s your baseline — you can expect that order of magnitude of bugs in the initial release of your rewrite. My point was that the test suite you start wit

> That’s your baseline — you can expect that order of magnitude of bugs in the initial release of your rewrite. My point was that the test suite you start with for your rewrite will be (or at least should be) a lot better than the test suite you had when you started writing the original code. The spec will likely be better too. Also, you can learn a lot from the previous iteration. These effects, plus the benefits of the new language, have the potential to reduce the bug count dramatically. Maybe even by an order of magnitude. Having said that, you're certainly right that there are some steps back and the net cost or benefit is likely highly context-dependent. It would be great to have more data on projects that have done this, to help people estimate the costs and benefits in their context.