In episode 72 of Thinking Elixir, we talk with Wiebe-Marten Wijnja about his project TypeCheck that provides a new kind of runtime type checking for Elixir applications. The syntax builds on your existing spec types so it still works for dialyzer but adds additional compile time created checks. It also works for generating property based test data. This feature comes out in a new ability called “spectest”. Like doctests, you can have automated checks that verify the function adheres to the spec! We also cover how TypeCheck allows writing type declarations for other libraries like Ecto and Plug. There are some interesting ways for people to contribute! A very interesting library!