Maybe it’s just because my expectations are shaped with my usage of Go, but I pretty much expect any modern language designed for writing non-trivial applications to have unit test support built-in nowadays.

Which is why it’s a bit surprising to see a language as opinionated as Elm that doesn’t include a core test package and test runner out of the box. I had to download a third-party test runner and install a non-core package to write and run unit tests. Not difficult to do, but still quite an uncharacteristic, JavaScript-esc approach to supporting this aspect of development in an otherwise integrated language toolkit.