def test_feature_times_unspecified_training_inputs_error(self):
        """
        Tests that `_get_feature_times` throws correct error when
        `target_series` and/or `output_chunk_length` hasn't been
        specified when `is_training = True`.
        """
        output_chunk_length = 1
        # Don't specify `target_series`:
        with pytest.raises(ValueError) as err:
            _get_feature_times(
                output_chunk_length=output_chunk_length, is_training=True
            )
        assert ("Must specify `target_series` when `is_training = True`.") == str(
            err.value
        )
        # Don't specify neither `target_series` nor `output_chunk_length`
        with pytest.raises(ValueError) as err:
            _get_feature_times(is_training=True)
        assert ("Must specify `target_series` when `is_training = True`.") == str(
            err.value
        )

        Tests that `_get_feature_times` throws correct error when
        `target_series` and/or `output_chunk_length` hasn't been
        specified when `is_training = True`.
        
darts/tests/utils/tabularization/test_get_feature_times.py