When I add some junk to application.js I get following error from Poltergeist:
Capybara::Poltergeist::JavascriptError: One or more errors were raised in the Javascript code on the page. If you don't care about these errors, you can ignore them by setting js_errors: false in your Poltergeist configuration (see documentation for details).
However when I just throw and exception, it's ignored (and test fails because of page functionality missing). Can I make Poltergeist fail if page has unhandled exceptions? Or at least issue warnings?
That sounds like a bug to me - please report it on Github with steps to reproduce.