def _my_trans(data):
    data_t = fft(data)
    data_t = np.concatenate([data_t[:, :, None], data_t[:, :, None]], axis=2)
    return data_t, None
FFT that adds an additional dimension by repeating result
dataset/ETHPy150Open mne-tools/mne-python/mne/tests/test_source_estimate.py/_my_trans