You can write many other other kinds of automated tests. Unit tests are rarely worth it, since they only look at the code in isolation, and often miss the forest for the trees if they're the only kind of test you have. But then, if you have other higher level tests that test your components are working well together, they're already implicitly covering that each component individually works well too - so your unit tests for that component are just duplicating the work the integration tests are already doing.

Sometimes you really need to ensure that something is a tree. And you do not need the whole forest around for that. Sure you can’t have an adventure with only a tree. But if you need a tree, you need to make sure someone don’t bring a concrete tree sculpture.