'Any unrelated content in the ``~/.ssh/authorized_keys`` file is left in
place by ``configure_ssh``.'

def test_existing_authorized_keys_preserved(self):

    existing_keys = 'ssh-dss    AAAAB3Nz1234567890    comment\nssh-dss    AAAAB3Nz0987654321    comment\n'
    ssh_path = self.server.home.child('.ssh')
    ssh_path.makedirs()
    authorized_keys = ssh_path.child('authorized_keys')
    authorized_keys.setContent(existing_keys)
    configuring = deferToThread(self.configure_ssh, self.server.ip, self.server.port)
    def configured(ignored):
        self.assertIn(existing_keys, authorized_keys.getContent())
    configuring.addCallback(configured)
    return configuring
