By default, if you click a link through Capybara and it takes you into an external site, the current_url will work fine, but the content on the page does not change.
RackTest is the Capybara's default driver and it has its limitations.
you cannot use the RackTest driver to test a remote application, or to access remote URLs
If you really need to do that know other drivers features and try them.
h/t by Nick PalaniukTweet