def METHOD_NAME(datafile='data/gaff2.xml'):
    """
    Checks that function returns real path
    Parameters
    ----------
    datafile : str, default 'data/gaff2.xml'
    """
    from perses.utils.data import get_data_filename
    import os
    path = get_data_filename(datafile)
    assert os.path.exists(path), "Either path to datafile is broken, or datafile does not exist"