def test_shared_times_bounds_unspecified_inputs(self):
        """
        Tests that `get_shared_times_bounds` correctly handles case unspecified
        inputs (i.e. `None`) are passed. If passed with a specified series, the
        `None` input should be ignored, meaning that the returned bounds should
        be the start and end times of the only specified series. If only `None`
        inputs are passed, `None` should be returned.
        """
        # `None` is passed alonside a non-`None` input:
        series = linear_timeseries(start=0, length=5, freq=1)
        expected = (series.start_time(), series.end_time())
        assert get_shared_times_bounds(series, None) == expected
        assert get_shared_times_bounds(None, series) == expected
        assert get_shared_times_bounds(None, series, None) == expected

        # `None` should be returned if no series specified:
        assert get_shared_times_bounds(None) is None
        assert get_shared_times_bounds(None, None, None) is None

        Tests that `get_shared_times_bounds` correctly handles case unspecified
        inputs (i.e. `None`) are passed. If passed with a specified series, the
        `None` input should be ignored, meaning that the returned bounds should
        be the start and end times of the only specified series. If only `None`
        inputs are passed, `None` should be returned.
        
darts/tests/utils/tabularization/test_get_shared_times_bounds.py