'Errors in mounting raise a ``MountError``.'

def test_mount_unformatted(self):

    blockdevice = self._get_free_blockdevice()
    mountpoint = self._get_directory_for_mount()
    with self.assertRaisesRegexp(MountError, blockdevice.path):
        self.manager_under_test.mount(blockdevice, mountpoint)
