Unit tests enforce good design and naturally provide decent documentation on how components fit together. Unit tests also allow you to spend a bit more time on

Unit tests enforce good design and naturally provide decent documentation on how components fit together. Unit tests also allow you to spend a bit more time on the details of each component and find issues you'd otherwise find in production. If nothing else at least have some integration tests so that you can confidently refactor knowing that you're not breaking existing functionality somewhere.