Assert the existence of a HTML form that submits to the given URL.

def see_form(self, url):
    """
    Assert the existence of a HTML form that submits to the given URL.
    """

    elements = ElementSelector(
        world.browser,
        str('//form[@action="%s"]' % url),
        filter_displayed=True,
    )
    if not elements:
        raise AssertionError("Expected form not found.")