def METHOD_NAME(self):
    obj = self.df
    for subset in [
        "REE",
        "REY",
        "elements",
        "oxides",
        "isotope_ratios",
        "compositional",
    ]:
        with self.subTest(subset=subset):
            out = getattr(obj.pyrochem, subset)
            self.assertIsInstance(out, obj.__class__)  # in this case a dataframe