def raw_tmp(raw_clean_detrend):
    """Return an unmodified copy of the `raw_clean_detrend` fixture.

    This is run once per NoisyChannels test, to keep any modifications to
    `raw_tmp` during a test from affecting `raw_tmp` in any others.

    """
    raw_tmp = raw_clean_detrend.copy()
    return raw_tmp