def METHOD_NAME(self):
    """Check that the MD_POS_COR is subtracted from the original value"""
    with self.assertRaises(ValueError):
        self.focus_tracker.updateMetadata({model.MD_POS_COR: "booo"})
    # Subtract a big enough value that it's always negative
    self.focus_tracker.updateMetadata({model.MD_POS_COR: 10e-3})
    pos_cor = self.focus_tracker.getMetadata()[model.MD_POS_COR]
    self.assertAlmostEqual(pos_cor, 10e-3)
    pos = self.focus_tracker.position.value["z"]
    self.assertLess(pos, 0)
    self.focus_tracker.updateMetadata({model.MD_POS_COR: 0})