I found one study[1] which concludes that unit tests are not enough to reveal all errors which would be revelead when using a statically typed language.
1. https://docs.google.com/file/d/0B5C1aVVb3qRONVhiNDBiNUw0am8/...
Isn't it why Python guys are trying to use more annotations? To patch it with some sort of semi-decent static analysis?
Check the Dropbox's pain presentation: https://www.dropbox.com/s/83ppa5iykqmr14z/Py2v3Hackers2013.p...
> code needs more debugging, it is harder to maintain and overall productivity is lower
References?