And as I said in the other comment, tests won't catch all of the mistakes that static typing will catch anyway.
The partial type systems found in languages people actually use, though, only constrain the most glaring of mistakes that you are almost never going to make. Not impossible that you could make one, but highly unlikely. Certainly not on the order of "lots". More like once in a blue moon.
Refactoring is a different story. Having an editor that lights up like a Christmas tree when code changes breaks existing relationships is a huge boon, and with good refactoring tools you almost never have to break the relationships in the first place. This is where (partial) static typing truly shines.
Not true. People make these mistakes all the time.
I was literally reviewing code today where someone write Python code to write a field that didn't exist. They didn't realise because they hadn't written a test. They asked me to check if it fixed my issue, which wasted 5 minutes of my time checking, when an IDE with static types would have told them their mistake instantly.
You can pull the "well I don't make mistakes" classic, but it doesn't matter. People do make these mistakes.
I linked an empirical study showing that 15% of bugs are precisely these mistakes. If you don't think it's worth eliminating 15% of bugs then frankly I just think you have crazy priorities and I can't really fix that.
