input: 
  def classify_emails(X_train, y_train, X_test):
      """Construct a naive bayes classifier using scikit-learn's GaussianNB to classify emails as spam or not spam.
      >>> X_train = [[1], [2], [3], [4]]
      >>> y_train = [0, 0, 1, 1]
      >>> X_test = [[1], [3], [5]]
      >>> classify_emails(X_train, y_train, X_test)
      [0, 1, 1]
      """
      from sklearn.naive_bayes import GaussianNB
      model = GaussianNB()
      model.fit(X_train, y_train)
      y_pred = model.predict(X_test)
      return y_pred
  
output:     from sklearn.naive_bayes import GaussianNB
      model = GaussianNB()
      model.fit(X_train, y_train)
      y_pred = model.predict(X_test)
      return y_pred