input: Write a python function to create and train a Gaussian Naive Bayes classifier using sklearn, and predict the output for a test set.
  assert gaussian_naive_bayes(X_train, y_train, X_test) == y_pred1
  assert gaussian_naive_bayes(X_train2, y_train2, X_test2) == y_pred2
  assert gaussian_naive_bayes(X_train3, y_train3, X_test3) == y_pred3
output: def gaussian_naive_bayes(X_train, y_train, X_test):
      from sklearn.naive_bayes import GaussianNB
      model = GaussianNB()
      model.fit(X_train, y_train)
      y_pred = model.predict(X_test)
      return y_pred