This was a comment from @Bob_Carpenter on the GitHub issue tracker
Major changes, like the refactor
Daniel took on, took year*s*. The reason it took so long is that
he insisted on having these tests (though apparently, they weren't
thorough enough, because we still broke the software).
The elapsed time was years, but it wasn't due to insistence or these tests. It was caught up in design. The end product, which is in now, is still a compromise on the design side and hopefully we can straighten it out over time.
I just wanted to make it clear that the tests were not the bottle neck.