collective.betterbrowser improves the plone.testing browser with the following, run inside your functional testcase: :

from collective.betterbrowser import new_browser

def test_all_the_things(self):
    browser = new_browser(self.layer)
    browser.login_admin()
    browser.show()

At which point your default browser opens, showing the state of browser with the ability to actually interact with the testing plone site in the background.