You should be testing regardless of the strength of your type system. But testing with a weak type system isn't going to give you anywhere near the guarantees

You should be testing regardless of the strength of your type system. But testing with a weak type system isn't going to give you anywhere near the guarantees you'd get from a well-designed type system in addition to testing: https://kevinmahoney.co.uk/articles/tests-vs-types/ https://kevinmahoney.co.uk/articles/tests-vs-types/