code: def test_theta_1():
      # with theta = 1 Theta-line is equal to the original time-series
      y = load_airline()
      t = ThetaLinesTransformer(1)
      t.fit(y)
      actual = t.transform(y)
      np.testing.assert_array_equal(actual, y)
  
imports: import numpy
  import pytest
  from scipy.stats import linregress
  from sktime.datasets import load_airline
  from sktime.transformations.series.theta import ThetaLinesTransformer
label_desc: Use image node_id 2 for calling a global function with example usage: test_theta_1() without return types