Regarding dialyzer: Yes, it's sane to use it although it's a massive PITA, especially when you have to collaborate with people who do not write type annotations

Regarding dialyzer: Yes, it's sane to use it although it's a massive PITA, especially when you have to collaborate with people who do not write type annotations or use such libraries. Regarding testing - I think it depends on the type of application you are writing. If you need 99.99% uptime, probably you have to have almost full test coverage. But for the kind of software that I write (at least lately), I rely on "let's make illegal states unrepresentable" to a large degree, then write a small number of regression tests (or fix the types) when we find bugs... This has proven (at least to me) to be good enough, especially compared to my clients' previous experience, which is usually very poor: extremely buggy software in a dynamic language with almost no tests and docs. Perfect quality is usually not needed or at least not worth the price.