When I wrote Ruby/Javascript, I remember needing to write unit tests that verified types of input/output variables. When I write in dynamically typed language

When I wrote Ruby/Javascript, I remember needing to write unit tests that verified types of input/output variables. When I write in dynamically typed language I never write tests like that. I'm more familiar with static than dynamic, but are experts really doing that kind of thing? That'd be a case for design by contract.