You’re not alone — I am sure other people have done this before me but I haven’t ever seen it published, and I rediscovered this technique independently. The logic behind this library has been ported to both scala and typescript without issue, I hope you and others can benefit from the idea even if you don’t use my implementation.

It's really great. It reminds me of using overlay filesystems for tests so that you can maintain a clean read-only template and then run all your tests non-destructively on the overlay.