code: def test_generate_index(self):
      def test_routine(
          expected_length,
          expected_start,
          expected_end,
          start,
          end=None,
          length=None,
          freq=None,
      ):
          index = generate_index(
              start=start, end=end, length=length, freq=freq
          )
          assert len(index) == expected_length
          assert index[0] == expected_start
          assert index[-1] == expected_end
  
      for length in [1, 2, 5, 50]:
          for start in [0, 1, 9]:
              # test pd.RangeIndex with varying step sizes
              for step in [1, 2, 4]:
                  expected_start = start
                  expected_end = start + (length - 1) * step
                  freq = None if step == 1 else step
                  test_routine(
                      expected_length=length,
                      expected_start=expected_start,
                      expected_end=expected_end,
                      start=start,
                      length=length,
                      freq=freq,
                  )
  
                  test_routine(
                      expected_length=length,
                      expected_start=expected_start,
                      expected_end=expected_end,
                      start=start,
                      end=expected_end,
                      freq=step,
                  )
  
                  test_routine(
                      expected_length=length,
                      expected_start=expected_start,
                      expected_end=expected_end,
                      start=None,
                      end=expected_end,
                      length=length,
                      freq=step,
                  )
  
                  if start == 0:
                      continue
  
                  # test pd.DatetimeIndex with a start date within 01 and 09
                  start_date = pd.Timestamp(f"2000-01-0{start}")
                  dates = generate_index(
                      start=start_date,
                      length=length,
                      freq="D" if step == 1 else f"{step}D",
                  )
                  start_assert, end_assert = dates[0], dates[-1]
                  test_routine(
                      expected_length=length,
                      expected_start=start_assert,
                      expected_end=end_assert,
                      start=start_assert,
                      length=length,
                      freq="D" if step == 1 else f"{step}D",
                  )
                  test_routine(
                      expected_length=length,
                      expected_start=start_assert,
                      expected_end=end_assert,
                      start=start_assert,
                      end=end_assert,
                      freq="D" if step == 1 else f"{step}D",
                  )
                  test_routine(
                      expected_length=length,
                      expected_start=start_assert,
                      expected_end=end_assert,
                      start=None,
                      end=end_assert,
                      length=length,
                      freq="D" if step == 1 else f"{step}D",
                  )
  
      # `start`, `end` and `length` cannot both be set simultaneously
      with pytest.raises(ValueError):
          generate_index(start=0, end=9, length=10)
      # same as above but `start` defaults to timestamp '2000-01-01' in all timeseries generation functions
      with pytest.raises(ValueError):
          linear_timeseries(end=9, length=10)
  
      # exactly two of [`start`, `end`, `length`] must be set
      with pytest.raises(ValueError):
          generate_index(start=0)
      with pytest.raises(ValueError):
          generate_index(start=None, end=1)
      with pytest.raises(ValueError):
          generate_index(start=None, end=None, length=10)
  
      # `start` and `end` must have same type
      with pytest.raises(ValueError):
          generate_index(start=0, end=pd.Timestamp("2000-01-01"))
      with pytest.raises(ValueError):
          generate_index(start=pd.Timestamp("2000-01-01"), end=10)
  
file_path: darts/darts/tests/utils/test_timeseries_generation.py
imports: from typing import Union
  import numpy
  import pandas
  import pytest
  from darts import TimeSeries
  from darts.utils.timeseries_generation import autoregressive_timeseries, constant_timeseries, datetime_attribute_timeseries, gaussian_timeseries, generate_index, holidays_timeseries, linear_timeseries, random_walk_timeseries, sine_timeseries
label_desc: Use image node_id 7 for calling the TestTimeSeriesGeneration obj's underlying member method code with example usage: obj.test_generate_index() without return types