You use unit tests in Python and Javascript among other things to check for type/value in some places which can be easily avoided if you explicitly used types. Also I often see in imperative languages that unit tests are used to declaratively describe something which you had to imperatively implement. To me it often feels like declarative functional languages have these features immediately as you write the code but then you have to invest the mental effort up front so people rather do half the thinking first then wrap things up with unit tests. The problem is you have to go back to the initial code when wiritng unit tests which fail while you could have done the complete work the first time around. Often it feels like people don't want to do too much work so they choose the language which allows them to offload erorrs for later. It even makes business sense to finish sooner then charge for maintenance later. A shame really