code: def test_constant_timeseries(self):
      # testing parameters
      value = 5
  
      def test_routine(start, end=None, length=None):
          # testing for constant value
          constant_ts = constant_timeseries(
              start=start, end=end, value=value, length=length
          )
          value_set = set(constant_ts.values().flatten())
          assert len(value_set) == 1
          assert len(constant_ts) == length_assert
  
      for length_assert in [1, 2, 5, 10, 100]:
          test_routine(start=0, length=length_assert)
          test_routine(start=0, end=length_assert - 1)
          test_routine(
              start=pd.Timestamp("2000-01-01"), length=length_assert
          )
          end_date = generate_index(
              start=pd.Timestamp("2000-01-01"), length=length_assert
          )[-1]
          test_routine(start=pd.Timestamp("2000-01-01"), end=end_date)
  
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 1 for calling the TestTimeSeriesGeneration obj's underlying member method code with example usage: obj.test_constant_timeseries() without return types