I am glad you liked it and that it was thought-provoking.

You really got the point and didn't jump into implementation details and proposing better factory implementation.

I definitely see your point. I am still not 100% on the dynamic typing side but am getting there tho :D, maybe I am 80%-90% there.

Deploying both parts together is a good point but independent deployability is one of the most important qualities of good written software.

And yes, unit tests are totally different mechanism, outcome is the same but everything else is totally different. Comprehensive suite of unit tests can do wonders in a codebase tho. Unit tests give you ability to strengthen or weaken type constraints which I find pretty useful.