def METHOD_NAME(self):
    """Make sure the part load factor is always positive."""
    part_load_ratios = np.arange(0.0, 1.1, 0.1)
    part_load_factors = np.vectorize(calc_CT_partload_factor)(part_load_ratios)
    self.assertGreaterEqual(part_load_factors.all(), 0.0)