To achieve the same level of quality, yes you absolutely do. This is actually a fairly fundamental fact about static typing. Static typing is a weak form of formal verification, or equivalently formal verification is just really really strong static typing. Clearly you don't need to write as many tests for formally verified code. The same is true (to a lesser extent) for "ordinary" static typing.

> Sure, I've seen developers do all kinds of stupid things too.

It's not stupid if you have a static typing system available! The stupidity was relying on tests to verify types, instead of ... you know, the thing whose whole purpose is to verify types.