old_contents: import unittest
  
  from sklearn import datasets
  from xgboost import XGBClassifier
  
  class TestXGBoost(unittest.TestCase):
      def test_classifier(self):
          boston = datasets.load_boston()
          X, y = boston.data, boston.target
  
          xgb1 = XGBClassifier(n_estimators=3)
          xgb1.fit(X[0:70],y[0:70])
  
new_contents: import unittest
  
  import xgboost
  
  from distutils.version import StrictVersion
  from sklearn import datasets
  from xgboost import XGBClassifier
  
  class TestXGBoost(unittest.TestCase):
      def test_version(self):
          # b/175051617 prevent xgboost version downgrade.
          self.assertGreaterEqual(StrictVersion(xgboost.__version__), StrictVersion("1.2.1"))
  
      def test_classifier(self):
          boston = datasets.load_boston()
          X, y = boston.data, boston.target
  
          xgb1 = XGBClassifier(n_estimators=3)
          xgb1.fit(X[0:70],y[0:70])
  
subject: Add xgboost version regression test.