[marcosdumay]

It's reasonably strong, so that on practice you can trust it to verify the properties it verifies. (Though, it's not completely flawless in theory.)

It's also static, so your types declarations will replace tests.

But it's extremely inexpressive, so you can declare very few properties, and so it will replace very few tests.

And it's inflexible, so it will get on your way all the time while you program.

Anyway, I can almost guarantee you the GP wasn't talking about Java.