def METHOD_NAME(self):
    wizard = (
        self.env["split.contract"]
        .with_context(active_id=self.contract3.id)
        .create({})
    )
    # set quantity to split in the wizard
    with self.assertRaises(ValidationError):
        wizard.split_line_ids[0].quantity_to_split = (
            wizard.split_line_ids[0].original_qty + 2
        )