Elixir does an amazing job of showing you why a test failed, but as for debugging, up until the latest release, 1.5, there wasn't really a debugger, it had pry, which lets you play around in the environment at the point where pry is called, but you can't step though code. 1.5 introduced a more useful debugging experience, but you can't step line by line, you can only step from breakpoint to breakpoint as far as I'm aware, but I haven't played much with it yet. It's getting there though! I should note that I haven't really lamented the lack of a good debugger, and I came from .NET where I had one of the best debuggers available.