I inherited a python based build system which had been written without any unit tests because....it's a build system right? right?? Anyhow it was the kind of t

I inherited a python based build system which had been written without any unit tests because....it's a build system right? right?? Anyhow it was the kind of thing where you'd build for 20 minutes (Android) and then have some kind of trivial error in the python code at the end of the build. You fix that and run again and waste another 20 minutes on the next thing. I couldn't do unit tests all at once because of the design not having any way of accommodating them. I needed something to stop the enormous waste of time. So I added type hints. The IDE should show me when illogical things were being done with parameters to methods/functions. It was fairly quick compared to a total refactoring but not effort free. I barely noticed any effect. Didn't catch a single error. Eventually I created a kind of dummy version of Android that "built" in a few seconds and I tested against that first. That allowed me to speed up changes and get some refactoring done to make a few critical unit tests and the whole thing started to get under control. This anecdote has almost no meaning - you cannot conclude that type hints have no benefit because of one case - I just think that tests are almost always more important and hinting and the whole rigmarole of strong typing are much less of a panacea than tests are.