“We don’t need types
“We don’t need types. We write tests.”
Tests are wonderful. But tests don’t replace types.
Why? Because tests are harder to do well than types.
Teams often struggle to write fast, reliable, useful tests. I often see tests that don’t fully cover the feature, or even test what they claim to test!
Sure, teams make typing mistakes too. But typing mistakes are typically less frequent, more obvious, and easier to catch via automated tools.
Types are basically “easy” tests. So, the team is more likely to use types well than they are to write solid tests.
In summary, write tests. But even with many good tests (which is both hard and rare), types remain useful.