def test_shared_times_unspecified_inputs(self):
        """
        Tests that `get_shared_times` correctly handles unspecified
        (i.e. `None` value) inputs. If `None` is passed with another
        series/time index, then `None` should be ignored and the time
        index of the other series should be returned. If only `None`
        values are passed, `None` should be returned.
        """
        # Pass `None` with series/time index input:
        series = linear_timeseries(start=pd.Timestamp("1/1/2000"), length=5, freq="d")
        assert get_shared_times(None) is None
        assert series.time_index.equals(get_shared_times(series, None))
        assert series.time_index.equals(get_shared_times(None, series, None))
        assert series.time_index.equals(get_shared_times(None, series.time_index, None))
        # Pass only `None` as input:
        assert get_shared_times(None) is None

        Tests that `get_shared_times` correctly handles unspecified
        (i.e. `None` value) inputs. If `None` is passed with another
        series/time index, then `None` should be ignored and the time
        index of the other series should be returned. If only `None`
        values are passed, `None` should be returned.
        
darts/tests/utils/tabularization/test_get_shared_times.py