When using Capybara, sometimes you get an error you don't quite understand. Maybe there's a missing button or link you're trying to use, or the field you're trying to type in doesn't exist.
Sometimes, it would be easy to just get a quick glance at the page at the moment your test fails. If you're using Selenium, you could add a sleep, but that probably wouldn't give you enough time to figure out what's going wrong.
Going through Capybara’s source last week, I found the save_and_open_page methoid, which saves the current page —complete with styling and images— and opens it in your favorite browser:
it 'should register successfully' do
visit registration_page
save_and_open_page
fill_in 'username', :with => 'jkreeftmeijer'
end