def _assert_equal_channels(axis):
    """check that all the trials have the same channels, in the same order.

    Parameters
    ----------
    axis : ndarray of ndarray
        one of the data axis

    Raises
    ------

    """
    for i0 in axis:
        for i1 in axis:
            if not all(i0 == i1):
                raise ValueError(
                    'The channels for all the trials should have the same labels, in the same order.'
                    )
