Tests are code and need to be maintained. Type systems remove the need for certain classes of tests that would otherwise need to be written and maintained. Just because you need to write other unit tests doesn't mean it's free to write unit tests to check types.
In general, if you reach a non trivial size of code you have to have unit tests in order to stay productive and speedy at a high quality level.
A type-system only speeds you up in the beginning.