code: def test_integer_indexed_series(self, mode):
      values_target = np.random.rand(30)
      values_past_cov = np.random.rand(30)
      values_future_cov = np.random.rand(30)
  
      idx1 = pd.RangeIndex(start=0, stop=30, step=1)
      idx2 = pd.RangeIndex(start=10, stop=70, step=2)
  
      preds = []
      for idx in [idx1, idx2]:
          target = TimeSeries.from_times_and_values(idx, values_target)
          past_cov = TimeSeries.from_times_and_values(
              idx, values_past_cov
          )
          future_cov = TimeSeries.from_times_and_values(
              idx, values_future_cov
          )
  
          train, _ = target[:20], target[20:]
  
          model = LinearRegressionModel(
              lags=[-2, -1],
              lags_past_covariates=[-2, -1],
              lags_future_covariates=[0],
              multi_models=mode,
          )
          model.fit(
              series=train,
              past_covariates=past_cov,
              future_covariates=future_cov,
          )
  
          preds.append(model.predict(n=10))
  
      # the predicted values should not depend on the time axis
      np.testing.assert_equal(preds[0].values(), preds[1].values())
  
      # the time axis returned by the second model should be as expected
      assert all(
          preds[1].time_index
          == pd.RangeIndex(start=50, stop=70, step=2)
      )
  
imports: import copy
  import functools
  import itertools
  import math
  from unittest.mock import patch
  import numpy
  import pandas
  import pytest
  from sklearn.ensemble import HistGradientBoostingRegressor, RandomForestRegressor
  from sklearn.linear_model import LinearRegression
  import darts
  from darts import TimeSeries
  from darts.dataprocessing.encoders import FutureCyclicEncoder, PastDatetimeAttributeEncoder
  from darts.logging import get_logger
  from darts.metrics import mae, rmse
  from darts.models import CatBoostModel, LightGBMModel, LinearRegressionModel, NotImportedModule, RandomForest, RegressionModel, XGBModel
  from darts.utils import timeseries_generation
  from darts.utils.multioutput import MultiOutputRegressor
label_desc: Use image node_id 23 for calling the TestRegressionModels obj's underlying member method code with example usage: obj.test_integer_indexed_series(mode) without return types