code: def test_subsample_regression_4k(self):
      rows = 4000
      X = np.random.rand(rows, 3)
      X = pd.DataFrame(X, columns=[f"f{i}" for i in range(3)])
      y = pd.Series(np.random.rand(rows), name="target")
  
      gft3 = GoldenFeaturesTransformer(self.automl_dir, REGRESSION)
      X_train, X_test, y_train, y_test = gft3._subsample(X, y)
  
      self.assertTrue(X_train.shape[0], 2000)
      self.assertTrue(X_test.shape[0], 2000)
      self.assertTrue(y_train.shape[0], 2000)
      self.assertTrue(y_test.shape[0], 2000)
  
imports: import unittest
  import tempfile
  import json
  import shutil
  import numpy
  import pandas
  from numpy.testing import assert_almost_equal
  from sklearn import datasets
  from supervised.preprocessing.goldenfeatures_transformer import GoldenFeaturesTransformer
  from supervised.algorithms.registry import BINARY_CLASSIFICATION, MULTICLASS_CLASSIFICATION, REGRESSION
label_desc: Use image node_id 4 for calling the GoldenFeaturesTransformerTest obj's underlying member method code with example usage: obj.test_subsample_regression_4k() without return types