You can have a program with correct type handling that doesn't work but with unit tests you have a program that works and documentation (in the form of the test

You can have a program with correct type handling that doesn't work but with unit tests you have a program that works and documentation (in the form of the test) about the ways in which the programmer expected it to work. That's why I find type hinting to be relatively high effort for relatively low benefit and choose to use it only where I feel it makes life better. The optionality suits me. It's a nice to have but that's all.