Imports and variables:

    >>> import plone.testing.z2 as helpers
    >>> from plone.app.testing import login, TEST_USER_NAME
    >>> app = layer.get('app')
    >>> portal = layer.get('portal')
    >>> request = layer.get('request')
    >>> portalURL = portal.absolute_url()
    >>> browser = helpers.Browser(app)
    >>> browser.handleErrors = False

    
The user visits the homepage with his browser
    >>> portal.changeSkin('GdacSkin', request)
    >>> browser.addHeader('plone_skin', 'GdacSkin')
    >>> browser.open(portalURL)

The top menu is displayed
    >>> browser.contents
    '...<ul id="portal-globalnavs">...'