code: def test_linear_timeseries(self):
      # testing parameters
      start_value = 5
      end_value = 12
  
      def test_routine(start, end=None, length=None):
          # testing for start value, end value and delta between two adjacent entries
          linear_ts = linear_timeseries(
              start=start,
              end=end,
              length=length,
              start_value=start_value,
              end_value=end_value,
          )
          assert linear_ts.values()[0][0] == start_value
          assert linear_ts.values()[-1][0] == end_value
          assert (
              round(
                  abs(
                      linear_ts.values()[-1][0]
                      - linear_ts.values()[-2][0]
                      - (end_value - start_value) / (length_assert - 1)
                  ),
                  7,
              )
              == 0
          )
          assert len(linear_ts) == length_assert
  
      for length_assert in [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 2 for calling the TestTimeSeriesGeneration obj's underlying member method code with example usage: obj.test_linear_timeseries() without return types